GE SUPERBUTE Instrument Transformers INSTRUCTIONS
SUPERBUTE™ Dry-type, Butyl-molded Instrument Transformers are designed to operate in both indoor and outdoor environments. They feature versatile mounting options and are practically impervious to moisture. These transformers are designed to meet IEEE C57.13 standards.
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GE
Digital Energy
INSTRUCTIONS
SUPERBUTE
™
Dry-type, Butyl-molded Instrument Transformers
GEH-230AG Issue 12/2014
Contents
Superbute Model Type & Catalog Numbers ............................................................................................................................................1
Low Voltage (600V – 1200V) .....................................................................................................................................................................................................1
Medium Voltage (2400V – 69000V) ........................................................................................................................................................................................1
Voltage Transformer Model Types ............................................................................................................................................................2
Current Transformer Model Types ............................................................................................................................................................3
Instructions ...................................................................................................................................................................................................4
Before Installation .......................................................................................................................................................................................4
Inspection ..........................................................................................................................................................................................................................................4
Storage & Handling ......................................................................................................................................................................................................................4
Testing ................................................................................................................................................................................................................................................4
Insulated-Neutral and Grounded-Neutral Terminal-Type Voltage Transformers ............................................................................................4
Demagnetizing Current Transformers .................................................................................................................................................................................5
Installation ....................................................................................................................................................................................................5
Safety Precautions ........................................................................................................................................................................................................................5
Mounting............................................................................................................................................................................................................................................6
Secondary Connections ..............................................................................................................................................................................................................6
Short-Circuiting of Current Transformers ...........................................................................................................................................................................7
Polarity ................................................................................................................................................................................................................................................7
High Altitude Operation .............................................................................................................................................................................................................7
Current Transformer Primary By-Pass Protection ..........................................................................................................................................................8
Primary Fuses for Voltage Transformers ............................................................................................................................................................................8
Selection Of Fuses – Voltage Ratings ...................................................................................................................................................................................9
Selection of Fuses – Ampere Ratings ............................................................................................................................................................................... 10
In-Service Maintenance ............................................................................................................................................................................11
Butyl Rubber Aging .................................................................................................................................................................................................................... 11
Cleaning .......................................................................................................................................................................................................................................... 12
Testing ............................................................................................................................................................................................................................................. 12
Interpretation Of Power-Factor And Megger Test Measurements ....................................................................................................................... 12
Disclaimer ...................................................................................................................................................................................................12
SUPERBUTE Model Type & Catalog Number
The figure at right illustrates the breakdown of a
SUPERBUTE Instrument Transformer model name, and the information contained therein. Assigned type numbers are described below.
J V W - 5 A
Special Feature (select models only)
A = High Accuracy
ER = High Accuracy, Extended Range
Low Voltage (600V – 1200V)
JAD - Current, Indoor/Outdoor, window
JAF - Current, Indoor, window, for switchgear
JAR - Current, Indoor, auxiliary
JCD - Current, Indoor/Outdoor, window
JCP - Current, Indoor/Outdoor, window
Correspond to IEEE Insulation
Classes as follows:
Voltage Class, in kV
0 = 0.6
1 = 1. 2
2 = 2.5
3 = 5
4 = 8.7
5 = 15
6 = 25
7 = 34.5
8 = 46
9 = 69
95 = BIL, in kV
110 = BIL, in kV
150 = BIL, in kV
200 = BIL, in kV
250 = BIL, in kV
350 = BIL, in kV
JCS - Current, Indoor, molded, for switchgear
JNP - Voltage, Indoor/Outdoor, US Navy
Medium Voltage (2400V – 69000V)
JCB - Current, Indoor, window
JCD - Current, Indoor/Outdoor, window type
JCM - Current, Indoor, bar type
JCW - Current, Indoor/Outdoor, bar type
JKC - Current, Indoor, wound primary, for switchgear
JKS - Current, Indoor, wound primary, for switchgear
JCK - Current, Outdoor, wound primary
JKM - Current, Indoor, wound primary
JKW - Current, Outdoor, wound primary
JVM - Voltage, Indoor, molded
JVW - Voltage, Outdoor, molded
JVS - Voltage, Outdoor, station-class, single bushing
JVT - Voltage, Outdoor, station-class, two bushing
Dominant Features;
(Dependent on second character)
M = Indoor
W = Outdoor
S = Single-bushing Voltage Transformer
T = Two-bushing Voltage Transformer
Current Transformer:
A = Window or Bar Type CT
C = Window or Bar Type CT
K = Wound Type CT
Voltage Transformer:
N = US Navy VT
V = Wound Type VT
Instrument Transformer:
= J
7 6 5 X 0 X X X X X
The figure at right illustrates the breakdown of a SUPERUBTE Instrument Transformer catalog number, and the information contained therein.
Group Number
Model
Voltage Class, in kV
0 = 0.6
1 = 1. 2
2 = 2.5
3 = 5
4 = 8.7
5 = 15
6 = 25
7 = 34.5
5 = Current Transformer
6 = Voltage Transformer
8 = 46
9 = 69
7 = Instrument Transformer
GEH-230AG
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J V W - 5 A
Correspond to IEEE Insulation
Classes as follows:
Voltage Class, in kV
Dominant Features;
(Dependent on second character)
M = Indoor
W = Outdoor
S = Single-bushing Voltage Transformer
T = Two-bushing Voltage Transformer
Current Transformer:
A = Window or Bar Type CT
C = Window or Bar Type CT
K = Wound Type CT
Voltage Transformer:
N = US Navy VT
V = Wound Type VT
Instrument Transformer:
= J
Voltage Transformer Model Types
GE Model
Catalog
# Series
Design
0.3 Acc.
Burden
JVM-2
JVM-3
JVM-4
JVM-5
JVM-6
JVW-3
JVW-4
JVW-5
JVW-110
JVW-6
JVW-6
JVW-7
JVS-150
JVT-150
JVS-200
JVT-200
JVS-250
JVT-250
JVS-350
JVT-350
762X022XXX
763X021XXX
764X020XXX
765X021XXX
766X021XXX
763X030XXX
764X030XXX
765X030XXX
765X031XXX
766X031XXX
766X035XXX
767X031XXX
766X030XXX
766X030XXX
767X030XXX
767X030XXX
768X030XXX
768X030XXX
769X030XXX
769X030XXX
---
---
---
---
---
Distribution-Class
Station-Class
Station-Class
Distribution-Class
Distribution-Class
Distribution-Class
Distribution-Class
Station-Class
Station-Class
Station-Class
Station-Class
Station-Class
Station-Class
Station-Class
Station-Class
Volts BIL (kV)
34,500
14,400
24,000
20,125
34,500
27,600
46,000
40,250
69,000
2,400
4,800
7,200
Indoor
45
60
75
14,400
24,000
95/110
Outdoor
125
4,800
7,200
14,400
14,400
24,000
24,000
60
75
110
110
125
150
150
150
150
200
200
250
250
350
350
Y
Y
Z
Z
Y
ZZ
ZZ
ZZ
ZZ
Y
ZZ
ZZ
ZZ
ZZ
Y
Y
Y
Y
Z
Z
Thermal
(VA)
750
750
1,500
1,500
750
750
3,000
3,000
3,000
3,000
5,000
4,500
5,000
4,500
750
1,500
1,500
1,000
750
750
140
230
225
240
235
420
520
430
560
44
105
105
105
95
95
Avg.
Lbs.
30
30
85
85
90
Other/
Options
Fuse Option
Fuse Option
Fuse Option
Fuse Option
---
2 Bushing
1-2 Bushing
1-2 Bushing
1-2 Bushing
1-2 Bushing
1 Bushing
1-2 Bushing
1 Bushing
2 Bushing
1 Bushing
2 Bushing
1 Bushing
2 Bushing
1 Bushing
2 Bushing
Notes:
1. Typical values shown. Actual values can vary with ratio. Contact factory or refer to data sheets.
2. High Accuracy versions are available in most models, designed with an “A” after the model name (e.g. JVW-5A).
Contact factory or refer to data sheets for performance values.
7 6 5 X 0 X X X X X
Group Number
Model
Voltage Class, in kV
5 = Current Transformer
6 = Voltage Transformer
7 = Instrument Transformer
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Current Transformer Model Types
GE Model
JCM-2
JCM-3
JCB-3
Catalog #
Series
752X020XXX
753X020XXX
753X021XXX
JCM-4 754X020XXX
JCB-4 754X021XXX
JCM-5 755X020XXX
JCB-5 755X021XXX
JKM-2
JKC-3
JKS-3
JKM-3
JKM-4
JKS-5
752X040XXX
753X002XXX
753X001XXX
753X040XXX
754X040XXX
755X001XXX
Design
Bar
Bar
Window
Bar
Window
Bar
Window
Wound
Wound
Wound
Wound
Wound
Wound
Volts
BIL
(kV)
0.3
Acc. @
Meter
Burden
Relay Class
Indoor – Window and Bar Types
2,500 45
5,000 60
5,000 60
B1.8
B1.8
B1.8
C200
C200
C100 - C400
Primary
Amps
Min.
600
600
600
Max.
4,000
4,000
4,000
Typical
30°C
R. F.
1.3
1.3
1.3
8,700 75
8,700 75
15,000 110
15,000 110
B1.8
B1.8
B1.8
B1.8
C200
C100 - C400
C200
C100 - C400
600
600
600
600
4,000
4,000
4,000
4,000
1.3
1.3
1.3
1.3
Indoor – Wound Types
2,500 45 B0.5
T50
5,000 60
5,000 60
B0.5
B0.1 –
B1.8
T50
T10 - T100
5,000 60
8,700 75
15,000 95
B1.8
B1.8
B0.1 –
B1.8
T100
T100
T10 - T100
10
10
15
5
10
15
1,200
1,200
800
800
800
800
1.5
1.5
1.5
1.5
1.5
1.5
JKM-5 755X042XXX
JCW-3 753X030XXX
JCD-3 753X031XXX
JCW-4 754X030XXX
JCD-4 754X031XXX
JCW-5 755X030XXX
Wound
Bar
Window
Bar
Window
Bar
15,000 110 B1.8
T200
Outdoor - Window and Bar Types
5,000
5,000
8,700
8,700
15,000
60
60
75
75
110
B1.8
B1.8
C100 - C400 600 4,000 1.3
B1.8
B1.8
B1.8
C200
C200
C100 - C400
C200
5
600 4,000 1.3
600
600
600
800
4,000
4,000
4,000
1.5
1.3
1.3
1.3
JCD-5 755X031XXX Window 15,000 110 B1.8
C100 - C400 600 4,000 1.3
Outdoor – Wound Types
JCK-3 753X051XXX Distribution-Class 5,000 60 B0.5
--5 800 3.0
JKW-3 753X050XXX Station-Class 5,000 60
JCK-4 754X051XXX Distribution-Class 8,700 75
JKW-4 754X050XXX Station-Class 8,700 75
JCK-5 755X052XXX Distribution-Class 15,000 110
JKW-5 755X053XXX Station-Class 15,000 110
JKW-6 756X050XXX Distribution-Class 25,000 150
B1.8
B0.5
B1.8
B0.5
B1.8
B1.8 or
B0.9
T100
---
T100
---
T200
T200 or T100
5
5
10
5
5
5
800
800
800
1.5
3.0
1.5
800 3.0
1,200 1.5
JKW-7 757X050XXX Distribution-Class 34,500 200
JKW-150 756X030XXX Station-Class 25,000 150
JKW-200 757X030XXX Station-Class 34,500 200
JKW-250 758X030XXX
JKW-350 759X030XXX
Station-Class
Station-Class
46,000 250
69,000 350
B0.5
B1.8
B1.8
B1.8
B1.8
---
T200/400
T200/400
T200/400
T200/400
Ave.
Lbs.
37
62
85
62
85
95
110
16
16
30
30
30
50
50
95
110
95
110
115
135
35
40
35
40
35
60
80
Other/
Options
---
Tap Sec.
Tap Sec.
Tap Sec.
Tap Sec.
Tap Sec.
Tap Sec.
---
---
Tap, Dual Sec.
Tap, Dual Sec.
---
Tap, Dual Sec.
Tap, Dual Sec.
Tap Sec.
Tap Sec.
Tap Sec.
Tap Sec.
Tap Sec.
Tap Sec.
Tap Sec.
Tap Sec.
Tap Sec.
Tap Sec.
10 800 3.0
72 Tap Sec.
25 3,000 1.5/3 320 Tap, Dual Sec.
25 3,000 2.0/ 345 Tap, Dual Sec.
25 3,000
25 3,000
2
2
540 Tap, Dual Sec.
590 Tap, Dual Sec.
Notes:
1. Multiply primary amps by rating factor to get maximum amp rating at 30ºC.
2. Typical values shown. Accuracy, Relay Class and Rating factor can vary with ratio.
3. High Accuracy and/or Extended Range versions are available in most models, designed with an “A” or “ER” after the model name (e.g. JKW-5A). Contact factory or refer to data sheets for performance values.
GEH-230AG
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Instructions
These instructions apply to SUPERBUTE current and voltage transformers with standard ratings and applied under usual conditions (refer to IEEE C57.13). For information on unusual ratings for frequency, voltage, current, or on installations where unusual conditions exist, please consult with a General Electric sales representative.
Before Installation
Inspection
Immediately upon receiving the transformer, inspect it for physical damage that may have occurred during shipment or handling. If damage is evident, file a claim with the transportation company immediately and promptly notify
General Electric sales representative.
For current transformers, make sure that the short-circuit jumper is securely in place on at least two terminals of each secondary provided. Do not remove or cut away a jumper until the secondary circuit in question is closed through a suitable burden.
Storage & Handling
The butyl-molded transformers are less fragile than porcelain, HCEP, and other epoxy insulated transformers, but nevertheless should be handled with care.
These butyl-modeled current transformers are practically impervious to moisture. If, due to unusual circumstances, insulations tests indicate a possibility of entrance moisture, please consult with a General Electric sales representative for detailed information on the proper procedure.
Testing
Insulation tests should be made in accordance with the latest revision of IEEE C57.13 Standard Requirements for
Instrument Transformers and/or ANSI/NETA ATS Standard for Acceptance Testing Specifications for Electrical Power
Equipment and Systems. Initial users tests of insulation should not be in excess of 75% of factory test voltage.
Insulated-Neutral and Grounded-Neutral Terminal-Type Voltage Transformers
Certain voltage transformers are designed with one fully insulated primary terminal, with the neutral end of the primary winding insulated for a lower level or connected to the case, frame, or base. In some designs, this connection to the case, etc., can be removed for primary-applied potential testing. In such designs, the customer should consider the required factory primary-applied potential test level to be 19 kV on outdoor types and 10 kV on indoor types. These levels correspond to IEEE C57.13 requirements for insulated-neutral terminal types.
GEH-230AG
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Demagnetizing Current Transformers
Current transformer cores may become magnetized as a result of the application of direct current to a winding
(for example, while measuring winding resistance or checking continuity) or in other ways. If a current transformer becomes magnetized, it should be demagnetized before being used for precision work. Current transformers should always be demagnetized before accuracy test. IEEE C57.13 lists methods for demagnetizing current transformers.
One method is to connect the transformer in the test circuit as shown in Fig. 1, below. Pass rated current through the low-turn winding (usually the primary). Increase the resistance (R) in the high-turn winding (usually the secondary) circuit unit the transformer core is saturated; then, slowly reduce resistance to zero and disconnect the current source.
Saturation of the core is indicated by a reduction of current in the high-turn winding circuit.
On tapped-secondary current transformers, demagnetizing should be done using the X2-X3 section of the winding to reduce the voltage required for saturation. On dual-secondary current transformers, the two secondaries should be paralleled during demagnetization.
WARNING: A CONTINUOUSLY VARIABLE RESISTANCE MUST BE USED TO AVOID OPENING THE HIGH-TURN WINDING
CIRCUIT WHEN RESISTANCE VALUES ARE CHANGED. AS THE RESISTANCE IS INCREASED, THE VOLTAGE ACROSS THE
RESISTANCE WILL APPROACH OPEN-CIRCUIT VALUE.
Current Transformer To Be Demagnitized
A
Current Source
(60 Hz)
Low-Turn
Winding
High-Turn
Winding*
R
*Note: The high-turn winding of a CT is the winding with the lower rated current.
Figure 1 - Circuit for demagnetizing current transformers
Installation
Safety Precautions
1. Always consider an instrument transformer as a part of the circuit to which it is connected, and do not touch the leads and terminals or other parts of the transformer unless they are adequately grounded.
2. The insulation surface of molded transformers should be considered the same as the surface of a porcelain bushing, since a voltage stress exists across the entire insulation surface from terminals to grounded metal parts.
3. Always ground the metallic cases, frames, bases, etc., of instrument transformers. The secondaries should be grounded close to the transformers. However, when secondaries of transformers are interconnected, there should only be one grounded point in this circuit to prevent accidental paralleling with system grounding wires.
4. Do not open the secondary circuit of a current transformer while the transformer is energized, and do not energize while the secondary circuit is open. Current transformers may develop open-circuit secondary voltages which may be hazardous to personnel or damaging to the transformer or equipment connected in the secondary circuit.
GEH-230AG
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5. The applications of power fuses in the primary circuits of voltage transformers is recognized and recommended operating practice on power systems. To provide the maximum protection practical against damage to other equipment or injury to personnel in the event of a voltage transformer failure, it is usually necessary to use the smallest fuse ampere rating which will not result in nuisance blowing. Increasing the fuse ampere rating to reduce nuisance blowing is usually accompanied by slower clearing and increased possibility of damage to other equipment or injury to personnel.
6. Never short-circuit the secondary terminals of a voltage transformer. A secondary short circuit will cause the unit to overheat and fail in a very short period of time.
Mounting
Versatile mounting is a feature of these transformers. All SUPERBUTE transformers can be mounted in any position: upright, horizontal, or even inverted. Instrument transformers should be mounted so that connections can be made to the power or distribution lines in such a manner as to avoid placing appreciable strains upon the terminals of the transformers.
For high-current transformer ratings, 2000 amperes and above, there may be some interference from the electric field of the return bus unless the bus centers are kept at a minimum distance of 15 inches apart; for ratings above 5000 amperes, this distance should be not less than 24 inches. If this type transformer is used with more than one primary turn, the loop should be at least 24 inches in diameter. Make sure that the secondary leads are twisted closely together and carried out without passing through the field of the primary conductors. It is not necessary that the bus exactly fill the window, but the bus or buses should be centralized. For ratings of 1000 amperes or less, these precautions are generally unnecessary.
Refer to model specific data sheets for more detail, as some models have maximum loading recommendations and/or alignment recommendations that should be followed. Several models have accessories available which allow for multiple mounting options such as bolting directly to a crossarm attached by “U” bolts or suspension hooks, or mounted on double crossarms, using channel brackets.
Secondary Connections
When connecting instrument transformers with meters or instruments, refer to the instructions furnished with the meters or instruments involved.
The resistance of all primary and secondary connections should be kept as low as possible to prevent overheating at the terminals, and to prevent an increase in the secondary burden.
The resistance of the secondary leads should be included in calculating the secondary burden carried by current transformers. The total burden should be kept within limits suited to the transformers used. The voltage drop in the primary and secondary leads of voltage transformers will reduce the voltage at the measuring device.
GEH-230AG
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Short-Circuiting of Current Transformers
Many current transformers are provided with a device for short-circuiting the secondary terminals, and are normally shipped from the factory with this device in the short-circuiting position. Check the position of the shorting device. The secondary terminals should be short-circuited by the shorting device, or equivalent, until a suitable burden (such as an ammeter, wattmeter, watthour meter, relay, etc.) has been connected to the secondary terminals.
Tapped-secondary current transformers, including multi-ratio current transformers with more than one secondary tap, are adequately short-circuited when the short is across at least 50 percent of the secondary turns. When a suitable secondary burden has been connected to two terminals of a tapped-secondary current transformer, and normal operation is desired, all unused terminals must be left open to avoid short- circuiting a portion of the secondary winding and producing large errors. Only one ratio can be used at a time.
On double-secondary or multiple-secondary current transformers, that is, transformers with two or more separate secondary windings (each having an independent core), all secondary windings not connected to a suitable burden must be shorted.
Before a burden is disconnected from a current transformer, the secondary terminals should be short- circuited.
Polarity
When wiring instrument transformer circuits, it is necessary to maintain the correct polarity relationship between the line and the devices connected to the secondaries. For this reason, the relative instantaneous polarity of each winding of a transformer is indicated by a marker H1 (or a white spot) on or near one primary terminal, and a marker X1 (or a white spot) near one secondary terminal. Refer to Figure 2.
Voltage Transformer
H1
X1
Current Transformer
H1 H2 Primary Current
Primary
Voltage
Secondary
Voltage
A
X1
Secondary
Current
X2
A
H2
X2
Figure 2 - Elementary Connections of Instrument Transformers
Where taps are present, all terminals are marked in order. The primary terminals are H1, H2, H3, etc.; the secondary terminals X1, X2, X3, etc. (and Y1, Y2, Y3, etc., if another secondary is used). The marker H1 always indicates the same instantaneous polarity as X1 and Y1.
When connection is made to secondary terminal having a polarity marking similar to a given primary terminal, the polarity will be the same as if the primary service conductor itself were detached from the transformer and connected directly to the secondary conductor. In other words, at the instant when the current is flowing toward the transformer in a primary lead of a certain polarity, current will flow away from the transformer in the secondary lead of similar polarity during most of each half cycle.
When the secondary of an instrument transformer is connected to an instrument (such as a voltmeter or ammeter) which measures only the magnitude of the primary voltage or current, polarity is not significant.
High Altitude Operation
These transformers are designed to operate over the ambient temperature range as indicated at the standard ratings
(see nameplate), provided the altitude does not exceed 3300 feet. If the transformers are to be used above 3300 feet, consult IEEE Standard C57.13 for the effect of altitude on temperature rise.
GEH-230AG
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Current Transformer Primary By-Pass Protection
Primary by-pass protectors are recommended for the proper protection of current transformers which are so located as to be exposed to the effect of surge currents. They are especially recommended for low primary-current ratings, as these ratings have a relatively high winding impedance. Thyrite primary by-pass protectors consist of one or more Thyrite disks which are connected in parallel with the primary winding of the transformer. When high frequency current surges occur, an appreciable part of the surge current is by-passed through the protector, reducing the voltage built up across the winding. Under normal operating conditions, the current bypassed has a negligible effect on accuracy.
On station-class current transformers (Types JKW-150 through JKW-350), internal gaps are provided on low current ratings. If high voltages occur across the primary coil, these gaps fire and bypass the current around most of the primary impedance. The gaps fire at voltages well below the internal turn-to-turn dielectric strength of the primary winding.
Primary Fuses for Voltage Transformers
The application of fuses in the primary circuits of voltage transformers is recognized and recommended operation practice of power systems. Their correct application is as important as the proper selection of power circuit breakers for such systems.
The function of voltage transformer primary fuses is to protect the power system by de-energizing failed voltage transformers. Although the function of the fuses is not to protect the voltage transformer, the fuses selected will often protect the voltage transformer promptly in the event of a short in the external secondary circuitry, if the short is electrically close to the secondary terminals.
To provide the maximum protection practical against damage to other equipment or injury to personnel in event of a voltage transformer failure, it is usually necessary to use the smallest fuse current rating which will not result in nuisance blowing. Fuses are rarely available which will fully protect voltage transformer from overloads, or immediately clear the system of a failed voltage transformer. Increasing the fuse ampere rating to reduce nuisance blowing is usually accompanied by slower clearing and increased possibility of other damage.
Voltage transformers require fuses which combine low continuous current rating with high interrupting capacity. In this regard, it will be noted that available interrupting ratings of current limiting power fuses in each voltage class are typically comparable to the available ratings of the related power circuit breakers.
In applying current-limiting fuses, it is necessary to adhere to certain established principles with respect to voltage, frequency, and interrupting ratings, as well as location and mounting.
The factors involved have been taken into consideration in listing the voltage transformers “with fuses” as listed in applicable Product Data Sheets.
The methods of connection fall into two classes, arbitrarily called Class I and Class II. Figure 3 shows various methods of connecting voltage transformers and primary fused to a power system.
Class I includes those connections in which each fuse carries the exciting current of only one transformer. This is the case in single-phase connection, (Figure 3, a) delta connections in which the transformer primaries are each fused separately (Figure 3, b and c), and wye connections (Figure 3, d).
Class III includes delta and open delta connections (Figure 3, e and f) in which a fuse must pass the exciting current of more than one transformer.
Class I
Class II
(a) Single-Phase (b) Delta (c) Open Delta (d) Wye
Figure 3. Primary Fuse and Voltage Transformer Connections
(e) Delta (f) Open Delta
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For indoor voltage transformers “with fuses”, listed on Product Data Sheets, the connections are necessarily Class
I, hence the fuses have been selected on the basis of Class I connections. On non-handbook items “with fuses”, the fuses are provided on the basis of Class I connections.
For outdoor voltage transformers where fuses are always mounted separately, Table 2 recommends fuse units for
Class I connections and for Class II connections.
The use of a fuse in the connection of a voltage transformer terminal to ground is not recommended. For grounded wye connections, it is preferred practice to connect one primary lead from each voltage transformer directly to the grounded neutral, using a fuse only in the line side of the primary. With this connection, a transformer can never be
“alive” from the line side with a blown fuse on the grounded side.
For separately mounted fuses where over-insulation is required or specified, the fuse must be selected on the basis of actual service voltage. The mounting for the fuse can be provided with insulators of a higher voltage rating so as to provide additional insulation to ground.
2,400
4,160Y
2,400
4,160Y
4,200
4,800
4,200
7,280Y
4,800
7,200
7,200
12,470Y
14,560Y
12,000
14,400
24,000
20,780Y
24,940Y
Selection Of Fuses – Voltage Ratings
Maximum operating line-to-line voltage should be in the range 70 to 100 percent of the rated voltage of the fuse.
This range of application voltage is recommended because the current-limiting action of the fuse is characterized by the generation of transient recovery voltages above normal circuit voltages values. The magnitude of these over-voltages increases nonlinearly as available short-circuit current increases. The maximum voltage permitted at rated interrupting current is specified in ANSI C37.46.
Therefore, it is important that the voltage rating of high-voltage fuses be coordinated with the voltage levels of the associated system equipment to avoid inducing destructive voltages during fuse operation.
Note: Fuse ratings apply to GE VT’s only.
System Voltage
Nominal
Line-to-line
DATA TABLE
Primary
Voltage
Fuse Voltage Rating
4,200
4,200
4,800
7,200
7,200
7,200
8,400
12,000
2,400
2,400
2,400
2,400
4,200
4,800
14,400
24,000
12,000
14,400
JVM-2
JVM-2
JVM-3
JVM-3
JVM-3
JVM-3
JVM-4
JVM-4
JVM-4
JVM-4
JVM-5
JVM-5
JVM-5
JVM-5
JVM-5
JVM-6
JVM-6
JVM-6
Fuse
Current Limiting Fuse Unit Type
1
Voltage Rating
Fuse
Size
2
Fuse Ampere Rating for Connection
Class I Class II
2,400
2,400
2,400
A, B or C
A, B or C
B or C
1E
1E
1E
2E
…
2E
4,800
4,800
4,800
4,800
7,200
4,800
7,200
7,200
B or C
B or C
B or C
B or C
B or C
B or C
B or C
B or C
1E
0.5E
0.5E
1E
2E
1E
1E
1E
2E
…
2E
2E
2E
…
1E
1E
14,400
14,400
14,400
14,400
23,000
23,000
23,000
B or C
B or C
B or C
B or C
C
C
C
1E
0.5E
0.5E
0.5E
0.5E
0.5E
0.5E
…
…
1E
0.5E
0.5E
—
—
1 Fuses selected must always have voltage rating equal to or nearest rating above the line-to-line voltage of the system.
Exception: Fuse units rated 600 volts may be applied on circuits rated 220 to 600 volts.
2
A- and B-size fuses can be mounted directly on the transformer. C-size fuses must be mounted separately.
Table 1. Recommended Fuses for Class I and II Indoor Connections
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System Voltage
Nominal
Line-to-line
12,470Y
14,560Y
12,000
14,400
24,000
20,780Y
24,940Y
34,500
34,500Y
23,000
34,500
24,940Y
34,500Y
7,280Y
4,800
7,200
7,200
12,470Y
14,560Y
12,000
14,400
2,400
4160Y
4,200
4,800
2,400
4160Y
4,200
DATA TABLE
Primary
Voltage
2,400
Fuse Voltage Rating
JVW-3
DATA TABLE
Fuse
Current Limiting Fuse Unit Type
1
Voltage Rating
Fuse
Size
Fuse Ampere Rating for Connection
2,400 C
Class I
1E
Class II
2E
2,400
4,200
4,800
JVW-3
JVW-3
JVW-3
4,800
4,800
4,800
C
C
C
1E
0.5E
0.5E
…
1E
1E
2,400
2,400
4,200
4,200
4,800
7,200
JVW-4
JVW-4
JVW-4
JVW-4
JVW-4
JVW-4
2,400
4,800
4,800
7,200
4,800
7,200
C
C
C
C
C
C
2E
2E
1E
2E
1E
1E
7,200
7,200
8,400
12,000
14,400
7,200
8,400
12,000
14,400
24,000
12,000
14,400
34,500
14,400
20,125
JVW-5
JVW-5
JVW-5
JVW-5
JVW-5
JVW-110
JVW-110
JVW-110
JVW-110
JVW-6
JVW-6
JVW-6
JVW-7
JVT-150
JVT-200
7,200
14,400
14,400
14,400
14,400
14,400
14,400
14,400
14,400
23,000
23,000
23,000
34,500
23,000
34,500
C
C
C
C
C
C
C
C
C
C
C
C
D
C
D
1 Fuses selected must always have voltage rating equal to or nearest rating above the line-to-line voltage of the system.
Exception: Fuse units rated 600 volts may be applied on circuits rated 220 to 600 volts.
1E
1E
0.5E
0.5E
0.5E
1E
0.5E
0.5E
0.5E
0.5E
0.5E
0.5E
1E
Table 2 - Recommended Fuses for Class I and II Outdoor Connections
1E
24,000 JVT-150 23,000 C 0.5E
34,500 JVT-200 34,500 D 1E
2E
1E
0.5E
0.5E
…
…
1E
…
0.5E
1E
…
…
2E
…
…
1E
0.5E
…
…
1E
…
2E
2E
3E
…
2E
Table 2 - Recommended Fuses for Class I and II Outdoor Connections
Selection of Fuses – Ampere Ratings
In selecting primary-fuse ampere ratings for use with voltage transformers, the objective is to use the smallest ampere rating that will not result in nuisance blowing during normal energization of the voltage transformer. When delayed clearing of a failed voltage transformer may result in damage to other equipment or injury to personnel, “Class II” connection (where a fuse must pass the magnetizing inrush current of two transformers) should be avoided if this connection requires a higher fuse ampere rating than the “Class I” connection (where a fuse passes the inrush current of one transformer).
In selecting primary fuses for voltage transformers the chief objectives are:
1. System short-circuit protection
2. Clearing the system of failed voltage transformers
3. Freedom from unnecessary fuse operation
To attain the first objective, it is necessary to use a fuse with interrupting rating at least equal to the maximum current obtainable in the system at the point of fuse installation.
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To attain the second objective with the maximum protection practical against damage to other equipment or injury to personnel, it is necessary to use the smallest fuse ampere rating which will not result in nuisance blowing. Fuses are rarely available which will fully protect the voltage transformer from overloads, or immediately clear the system of a failed voltage transformer. Increasing the fuse ampere rating to reduce nuisance blowing is always accompanied by slower clearing and the increased possibility of other damage.
To attain the third objective of freedom from unnecessary fuse blowing, it is necessary to choose fuses having sufficient inrush current capacity to safely pass the transformer magnetizing inrush.
The heat generated in the fuse line is proportional to the square of the current and the time during which it flows. It is logical, therefore, to evaluate the inrush capacity of the fuse in terms of the ampere-squared-seconds required to melt its current-responsive element. This may be written i
2 t, where “i” is the current flowing for “t” seconds.
The i 2 t inrush capacity of any fuse is readily obtained from the time-current curves of the fuses under consideration.
These curves are plotted on “log-log” paper, and it may be seen that, for fast melting at high currents, the meltingtime-current curve becomes practically a straight line with a negative slope of 2 to 1 (-63.43°). It is necessary only to project the straight-line portion of the curve back to the one-second line and square this current. Of course, the current from the straight-line portion of the curve, at any time, squared and multiplied by time will give the same result.
The maximum inrush current to the transformer can be recorded with an oscillograph, but the most practical way to get it is from the transformer manufacturer, in amperes-square-seconds. This may be written I 2 T, to distinguish it from the fuse i
2 t. For satisfactory fuse application, the fuse i
2 t should exceed the transformer I
2
T by a reasonable factor of safety. The recommended factor of safety is 1.5. Therefore, for Class I applications: i
2 t ≥ 1.5 I
2
T
For Class II applications, the fuse must pass the magnetizing current of two transformers and the heating effect of inrush in one line could be approximately three times that occurring for one transformer. Therefore, for Class II applications: i
2 t ≥ 4.5 I
2
T
The I
2
T of the transformers is typically calculated at 110% of rated primary voltage.
Possible damage to other equipment or injury to personnel, due to delayed clearing of a failed voltage transformer, is an important consideration, Class II connection should be avoided if this connection requires a higher fuse ampere rating than the Class I connection. It should be noted that in Class II (Figure 3, f), two of the fuses carry the excitation current of only one transformer. These two can be selected on the basis of Class I connections, provided approximately the same protection as provided in Class I (Figure 3, c).
The inrush I 2 T increases very rapidly with increases in applied voltages, and, in requesting the I 2 T value from the manufacturer, the voltage specified should be the maximum expected in service.
In some applications, particularly cable circuits, there is a possibility that the inherent capacitance of the circuit will give rise to a discharge current through the primaries of connected voltage transformers when the circuit is disconnected from the bus. The magnitude and duration of this discharge current may be calculated from the circuit constants, and in some instances may result in blowing of primary fuses. Such cases have been found to be rare, however, and for most installations, unnecessary operation of primary fuses can be prevented by selecting the fuse ampere rating on the basis of the magnetizing inrush current of the voltage transformers.
In-Service Maintenance
Whether mounted indoors or outdoors, SUPERBUTE transformers require no special care or regular maintenance other than keeping the insulation surfaces free from accumulation of dirt.
Butyl Rubber Aging
The only indication the HY-BUTE 60 butyl rubber material used in SUPERBUTE transformers gives of aging is a visual one, where the surface color turns from black to gray. The gray coloration that occurs on the surface of HY-BUTE 60 over a period of time is caused by ultra-violet radiations from sunlight. Most plastic materials, of which butyl is a part, start to decompose when subjected to ultra-violet radiation. With HY-BUTE 60, surface decomposition occurs slowly over a period of two to three years. In time, these decomposition products form a protective surface coating that prevents further penetration into the material. In HY-BUTE 60 the penetration is minute, being less than 1/64 of an inch.
The impact from this process is cosmetic only, as the decomposed surface product fully retains the non arc-tracking, hydrophobic, ozone resistance, and other environmental and electric characteristics of HY-BUTE 60 are while the transformer is in service.
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Cleaning
If the surface of the transformer should become contaminated with a foreign material or the customer desires to clean the surface of the transformer, the following procedure is recommended;
1. Scrub the surface of the transformer using a stiff brush and a mild detergent and water solution.
2. Rinse loose material from the surface with clean water.
3. If further cleaning is desired the mild detergent and water solution can be used in conjunction with grit cloth such as
Norton Abrasive Durite 421 – 320 GRIT.
4. It is not necessary to remove the gray coloration and restore the original black color. Removal of any “foreign” material should be sufficient in most instances.
5. Following the rinse process dry the transformer completely before testing
Note: it is no long recommended to apply silicone oil or any other surface restoration product to the transformer, as this may negatively impact the transformer insulation.
WARNING: CLEANING SHOULD ONLY BE PERFORMED WHILE UNIT IS DE-ENERGIZED.
Testing
These instrument transformers require no in service testing, and no test to date has proven to offer predictive value of internal insulation breakdown or remaining service life on SUPERBUTE designs. Testing on aged units can be performed at user’s discretion to validate units pass rated insulation and accuracy levels. Insulation tests should be made in accordance with the latest revision of IEEE C57.13 Standard Requirements for Instrument Transformers and/or ANSI/NETA ATS Standard for Acceptance Testing Specifications for Electrical Power Equipment and Systems. Periodic insulation tests by user should not be in excess of 65% of factory test voltage. These recommendations relate to dielectric tests applied between windings and ground and to induced voltage tests. For ratio and phase-angle tests, refer to IEEE C57.13.
Interpretation Of Power-Factor And Megger Test Measurements
The value of power-factor measurements in liquid-insulated transformers for monitoring development of certain failure mechanisms is well established. A common use of this test is to detect change in the level of contaminants in the liquid, allowing sufficient warning to have the unit serviced before failure. The insulation system of dry type SUPERUBTE instrument transformers is made with butyl and epoxy and is a chemically stable, sealed system, not subject to internal contamination.
In-service dry type transformers with high power factor readings are usually the result of surface contamination and or moisture (including inside the conduit box). This is a valid use of a power-factor test to schedule preventive maintenance.
When clean and free of moisture, dry-type instrument transformer power factor readings are invariably restored to original levels. The important distinction is that power-factor testing offers no predictive value of internal insulation breakdown.
A meggar test, while no more predictive, should be considered when trying to indentify weakened insulation. Neither power factor testing or megger testing are specified as a routine or type test in IEEE C57.13 Standard Requirements for Instrument
Transformers.
Disclaimer
These instructions do not purport to cover all details or variations in equipment nor to provide for every possible contingency to be met in connection with the installation, operation or maintenance. The equipment covered by these operating instructions should be operated and serviced only by competent technicians familiar with good safety practices, and these instructions are written for such personnel and are not intended as a substitute for adequate training and experience in safe procedures for this type of equipment. Should further information be desired or should particular problems arise which are not covered sufficiently for the purchaser’s purposes, the matter should be referred to the
General Electric Company.
GEH-230AG
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For more information about
GE’s Power Sensing products visit
GEDigitalEnergy.com/ITI
GE Digital Energy
Toll Free: +1 877-605-6777
Direct: +1 678-844-6777
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© 2014 General Electric Company. All rights reserved.
GEH-230AG (12/2014)
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Key features
- Dry-type, Butyl-molded
- Indoor/Outdoor operation
- Versatile mounting
- Moisture-resistant
- IEEE C57.13 compliant
