BECKWITH ELECTRIC M-3425, Instruction Book

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–19–
M-3425 Generator Protection Relay
M-3921 Field Ground Coupler
■
NOTES:
1. The above circuit measures insulation resistance (R
f
) between rotor field winding and ground (64F).
2. Relay injects
!
15 V squarewave (V
out
) and measures return signal (V
f
) to calculate R
f
.
3. The injection frequency can be set (0.1 to 1.0 Hz) based on the rotor capacitance, in order to improve
accuracy.
4. Analyzing signal rise time can determine if shaft brushes are open (64B).
Function Specification
Field/Exciter Supply Voltage Rating (Terminal (3) to (2)):
• 60 to 600 V dc, continuous
• 1000 V dc, 1 minute
Operating Temperature: –20° to +70°, Centigrade
Patent & Warranty
The M-3921 Field Ground Coupler is covered by a five year warranty from date of shipment.
Tests and Standards
M-3921 Field Ground Coupler complies with the following tests and standards:
Voltage Withstand
Isolation
4 kV ac for 1 minute, all terminals to case
Impulse Voltage
IEC 255–5, 5,000 V pk, 1.2 by 50
µ
s, 0.5 J, 3 positive and 3 negative impulses at 5 second
part 5 intervals per minute
Electrical Interference
Electrostatic Discharge Test
IEC 1000-4-2 Class 4 (8 kV)—point contact discharge
Fast Transient Disturbance Tests
IEC 1000-4-4 Class 4 (4 kV, 2.5 kHz)
Surge Withstand Capability
ANSI/IEEE 2,500 V pk-pk oscillatory applied to each independent circuit to earth
C37.90.1 2,500 V pk-pk applied between each independent circuit
5,000 V pk Fast Transient applied to each independent circuit to earth
5,000 V pk Fast Transient applied between each independent circuit
Radiated Susceptibility
ANSI/IEEE 25-1000 Mhz @ 20 V/m
C37.90.2
Atmospheric Environment
IEC 68–2–1 Cold, –20° C for 96 hours
IEC 68–2–2 Dry Heat, +70° C for 96 hours
IEC 68–2–3 Damp Heat, +40° C @ 93% RH, for 96 hours
Enclosure Protection
NEMA 1, IEC IPC-65