CRMagnetics Catalog

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123
Potential Transformers
G
Application Notes
3500 Scarlet Oak Blvd. St. Louis MO USA 63122 V: 636-343-8518 F: 636-343-5119
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Energy Monitoring
Company
ISO 9001:2008QualityManagementSystem
M N TI
1. Delta Connected Supply Systems
When applying voltage transformers to ungrounded delta connected supply systems, the transformer must not be connected in wye with the wye-point con-
nected to neutral ground, or ungrounded. The advent of zero sequence currents caused by a ground fault in the system will cause damage, and eventual
destruction of the transformer if the fault is not quickly removed.
2. Ferro resonance
Most voltage transformers are lightly loaded, particularly when associated with watthour metering and relaying schemes. If the voltage transformer has one
primary lead grounded, and during an abnormal condition creating a large overvoltage, the transformer may saturate, and its impedance may cause a res-
onance with the system capacitance. This resonance, or oscillation, may be sustained and could destroy the voltage transformer. If, however, the secondaries
are connected in delta, with a broken arrow, and a suitable resistor is connected across the broken corner, then ferro resonance can be damped. Our recom-
mendation for the resistive value is shown on the catalog sheet where it applies. The power rating is determined by the user.
3. Secondary Circuit Check
Immediately prior to connecting the burden and leads to the transformer, a check of the impedance at that circuit should be made. This will avoid a possible
short-circuit connection to the transformer, if a short-circuit is applied to the transformer, it can be withstood for one second. Note: Only secondary circuit
fuses can adequately protect the transformer from such a short circuit.
4. Primary Fuse Rating
Values shown are suggested for normal installations, in order to protect the system from a voltage transformer failure. Higher ratings at users option, may
be used to avoid unusual clearing due to conditions resulting from magnetizing in-rush.
ROUTINE FACTORY TESTS
VOLTAGE
CLASS NO. OF BUSHINGS CONNECTION LV 1 MIN
60Hz
H2 1 MIN
60Hz
HV 1 MIN
60Hz
INDUCED
18 SEC. 400Hz
5kV
1 L - GND N 2.5kV 10 kV NA 15kV OR 19kV
2 L - L 2.5kV NA 15kV OR 19kV DOUBLE VOLTAGE
8.7kV
1 L - GND N 2.5kV 10 kV NA 26kV
2 L - L 2.5kV NA 26kV DOUBLE VOLTAGE
15kV
1 L - GND N 2.5kV 10 kV NA 34 kV
2 L - L 2.5kV NA 34kV OR 36kV DOUBLE VOLTAGE
25kV
1 L - GND N 2.5kV 10 kV NA kV
2 L - L 2.5kV NA kV DOUBLE VOLTAGE
34.5kV
1 L - GND N 2.5kV 10 kV NA 70 kV
2 L - L 2.5kV NA 70kV OR 80kV DOUBLE VOLTAGE
Routine Factory Tests include: Polarity, accuracy, and partial discharge per CANADIAN STANDARDS (CAN3-C13-M83) (Partial discharge can also be carried out to IEC
requirements on request)
ANSI BURDEN DATA
CONNECTION VA POWER FACTOR ANGLE
W 12.5 0.10 84.3 °
X 25 0.70 45.6 °
M 35 0.20 78.5 °
Y 75 0.85 31.8 °
Z 200 0.85 31.8 °
ZZ 400 0.85 31.8 °