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SA-1 Generator Differential Relay - Class 1E
The percentage slope characteristic of the relay lim-
its the operating voltage on heavy external faults
where the performance of the two sets of current
transformers may be quite different.
On internal faults, the operating coil current is the dif-
ference of the current flowing in each of the windings
of the restraint transformer and sufficient operating
voltage is available to overcome the restraint voltage.
4.0 CHARACTERISTICS
The percentage slope curves are shown in Figures 8
and 9 (page 12 and page 13). It will be observed that
the relay operates at 5% unbalance at 5 amperes
restraint (Figure 8, page 12) to provide high sensitiv-
ity for internal faults up to full load conditions. At 60
amperes restraint, the operating current required to
trip the relay is 30 amperes or 50% unbalance (Fig-
ure 9, page 13). Thus, when 60 amperes through
fault current is flowing, the output of the main current
transformers may vary considerably without causing
incorrect operation.
The minimum pickup of the relay is 0.14 amperes.
The time curve of the relay is shown in Figure 10
(page 14).
The frequency response characteristic of the Type
SA-1 relay is shown in Figure 11 (page 15).
5.0 ENERGY REQUIREMENTS
5.1
EACH RESTRAINT CIRCUIT
Burden at 5 amperes is 0.25 VA
Continuous rating 20 amperes
1 second rating 300 amperes
5.2
OPERATING CIRCUIT
The burden imposed by the operating circuit on each
current transformer is variable because of the satu-
rating transformer. At 0.5 amperes, it is 1.48 ohms,
and at 60 amperes, it is 0.47 ohms.
Note that the neutral reactors are in series with the
operating coil circuit. They also have a saturating
characteristic, with a maximum impedance of roughly
80 ohms.
Continuous rating 10 amperes
1 second rating 200 amperes
5.3
AMPLIFIER
The dc burden on the station battery is:
Volts
Milliamperes
125 dc
48 dc
6.0 SETTINGS
There are no taps on either transformer and, conse-
quently, there are no settings to be made. The
48/125 Vdc relays are normally shipped for 125 volts.
For 48 Vdc applications use the mid tap on the resis-
tor mounted at the top of the relay. The red dot on the
resistor is the common point – DO NOT REMOVE.
7.0 INSTALLATION
The relays should be mounted on switchboard pan-
els or their equivalent in a location free from mois-
ture. 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 con-
nections 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 7 (page 11).
For detailed FT case information, refer to Instruction
Leaflet 41-076.
8.0 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 customer.
8.1
ROUTINE TEST
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 12 (page 15). Due to high imped-
ance of the external reactor, prior to saturation, the
test circuit of Figure 12 should be used to test the
relay only. The reactors can be checked by applying
41-348.11C
Watts
55
6.9
60
2.9
3
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