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3.6 Three-Phase Connections
The line connections for three-phase operations are shown in Figure 4.
Note the Type VR-1 regulator cannot be operated in Y connection with the
bank-neutral isolated. When these regulators are Y connected, the neutral
of the regulator bank must be effectively connected to the system neutral,
preferably by the fourth wire. Without this interconnection, Y connection is
hazardous, as the individual and independent voltage control of each phase
can cause unequal turn ratios between phases, resulting in shifting of an
isolated neutral with extreme distortion of phase voltages.
3.7 Short-Circuit Rating
The impedance of a regulator is practically negligible for reducing short-circuit
current. The impedance of the feeder up to the point at which the regulator is
installed should be sufficient to limit the short-circuit current in the regulator to
the value for which it is designed. It is recommended that feeder current-limiting
reactors be installed on the feeder to keep the short-circuit current within the
required limits.
Short-circuit rating on any position is 40 times the rated current at +10 percent regulation for 0.8 seconds. For short-circuit
duration above 0.8 seconds, the permissible short-circuit current is reduced to keep the product I²t product constant. In this
formula, "I" is the short-circuit current and "t" is the time in seconds. For instance, if the regulator is rated 2500 volts, 400
amperes, at +10 percent regulation, I²t = (400 x 40)² x 0.8 = 205 x 10⁶. For a short-circuit duration of 2 seconds,
2I² = 205 x 10⁶ and I = 10,100 amperes.
3.8 Overloading Single-phase Step Voltage Regulators
The regulator can be overloaded in accordance with the ANSI Guide for Loading Step Voltage Regulators, Appendix C57.95-
1984.
3.9 Power Connections
The Type VR-1 single-phase step voltage regulator may be connected in single or three-phase circuits in accordance with
the connections shown in Figure 5. For these connections, proper grounds, surge arresters and bypass switching devices
suitable for the line current are used. The regulator must also be on the neutral position. Before proceeding, the following
precautions are necessary:
1.
Regulator must be permanently grounded using grounding provision. Do not remove ground conductor while
the regulator is energized. Grounding conductor size should be in accordance with National Electrical Code
requirements.
2.
To avoid damage to windings, the bypass switch "A" must never be closed with load current flowing through the
regulator unless the regulator is first brought to the neutral position and the control power turned OFF. In closed
delta banks:
a. All three regulators must be operated to the neutral position.
b. The control power turned OFF
c. All units bypassed before removal of any unit from service.
3.
Device "D" must always be closed first when connecting the regulator into service and opened last when
removing the regulator from service to prevent possible injury to personnel or damage to the regulator due to
abnormal voltage peaks.
prolec.energy/prolecge
GEH-7299A: Installation, Operation and Maintenance Manual
for Type VR1™ Single-Phase, Step Type Regulators
Figure 5. Distribution Surge Arrester
11
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