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Type SA-1
Generator Differential Relay
4. CHARACTERISTICS
The percentage slope curves are shown in Figures
12 and 13. It will be observed that the relay operates
at 5% unbalance at 5 amperes restraint (Figure 12)
to provide high sensitivity for internal faults up to full
load conditions. At 60 amperes restraint, the operat-
ing current required to trip the relay is 30 amperes or
50% unbalance (Figure 13). Thus, when 60
amperes through-fault current is flowing, the output
of the main current transformers may vary consider-
ably without causing incorrect operation.
The minimum pickup of the relay is 0.14 ampere or
0.5 ampere for the desensitized version.
The operating characteristic of the desensitized SA-
1 is shown in Figure 14.
The time curve of the relay is shown in Figure 15.
The frequency response characteristic of the SA-1
relay is shown in Figure 16.
5. ENERGY REQUIREMENTS
Each Restraint Circuit
Burden at 5 amperes is 0.25 VA
Continuous rating 20 amperes
1 second rating 300 amperes
Operating Circuit
The burden imposed by the operating circuit on
each circuit transformer is variable because of the
saturating transformer and reactors. At 0.5 amperes,
it is 0.37 VA, and at 60 amperes it is 170 VA.
Continuous rating 10 amperes
1 second rating 200 amperes
Amplifier
The dc burden on the station battery is:
Volts
Milliamperes
125 dc
48 dc
Watts
55
6.9
60
2.9
6. SETTINGS
There are no taps on either transformer and, conse-
quently, there are no settings to be made except for
the choice of battery voltage level.
The 48/125 Vdc relays are normally shipped for 125
volts. For 48 Vdc applications use the mid-tap on the
resistor mounted at the top of the relay. The red dot
on the resistor is the common point – DO NOT
REMOVE.
7. INSTALLATION
The relay should be mounted on switchboard panels
or their equivalent in a location free from moisture.
Mount the relay vertically by means of the four
mounting holes on the flange for semi-flush mount-
ing.
Either a mounting stud or the mounting screws may
be utilized for grounding the relay. The electrical
connections may be made directly to the terminals
by means of screws.
The external reactor assembly should be mounted
and wired per "interwiring Connection Drawing", Fig-
ure 11.
For detailed FT case information, refer to I.L. 41-
076.
8. ADJUSTMENTS AND MAINTENANCE
The proper adjustments to insure correct operation
of this relay have been made at the factory and
should not be disturbed after receipt by the cus-
tomer.
8.1. R
T
OUTINE
EST
The following check is recommended to insure that
the relay is in proper working order. All checks can
best be performed by connecting the relay per the
test circuit of Figure 17. Due to high impedance of the
external reactor, prior to saturation, the test circuit of
Figure 17 should be used to test the relay only. The
reactors can be checked by applying 0.2 amperes 60
hertz and reading the voltage drop across the reactor
with a high impedance True RMS reading voltmeter.
The voltage drop will be between 20 and 26 volts
True RMS. For 0.4 amperes input, the reading
should be between 29 and 31 volts True RMS.
41-348.1H
3
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