41-348.1H
4
Type SA-1
Generator Differential Relay
1.
Minimum Trip Current with I
R
set at zero
amperes, apply 0.14
±
5% (0.5
±
5% got desensi-
tized SA-1) amperes operating current to each
operating circuit of the relay. The relay should
operate and the indicator lamp should light.
2.
Differential Characteristic
a) Apply I
R
of 5 amperes and adjust the operat-
ing current until the relay operates. The relay
should operate and the indicator lamp should
light with an operating current of 0.25
±
5%
amperes (0.71 5% for desensitized SA-1).
Repeat for each phase of the relay.
b) Apply I
R
of 60 amperes and adjust the oper-
ating current until the relay operates. The
relay should operate and the indicator lamp
should light with an operating current of
30
±
10% amperes. Repeat for each phase of
the relay. (I
R
= 40 amperes and I
O
=
24
±
10% for desensitized SA-1).
8.2. M
AINTENANCE
All relays should be checked once a year to detect
any failures which may have occurred. The tantalum
capacitors C1, C2, C3, C4 and C13 may have a com-
mon mode failure characteristic and should be
checked visually for symptoms of electrolyte leakage
every year and replaced if necessary.
8.3. C
ALIBRATION
Use the following procedure for calibrating the relay if
the relay adjustments have been disturbed. This pro-
cedure should not be used until it is apparent the
relay is not in proper working order.
1.
Minimum Trip Current – Connect the relay per
test circuit of Figure 17 with switch K open.
Adjust the operating resistor in the rear of the
relay until the relay operates with IO equal to
0.14 ampere, 0.5 ampere for desensitized SA-1.
DO NOT make adjustments to the resistor
unless the dc is disconnected.
The indicator lamp should light when the relay
operates.
Repeat for each phase of the relay.
2.
Percentage Slope Characteristic (Low Cur-
rent). Close switch K and set I
R
equal to 5
amperes and adjust the restraint resistor in the
rear of the relay until the relay operates with I
o
=
0.25
±
.010 amperes. DO NOT adjust resistor
with dc applied to relay.
The indicator lamp should light when the relay
operates.
Repeat for each phase of the relay.
Percentage Slope Characteristic (High Cur-
rent) – Set I
R
equal to 60 amperes for the oper-
ating current of 30 amperes. Replace the resistor
R17 if necessary. The value of R17 can be
between 0 and 100 ohms. Repeat for the other
two phases if necessary, replacing R18 and R19
respectively.
3.
Electrical Checkpoints – See Table 1.
9. RENEWAL PARTS
Repair work can be done most satisfactorily at the
factory. However, interchangeable parts can be fur-
nished to customers who are equipped for doing
repair work. When ordering parts, always give the
nameplate data.
10. ELECTRICAL CHECKPOINTS
Connect relay per test circuit of Figure 17. All voltage
readings should be made with a high resistance volt-
meter. Refer to component location of checkpoints.
Voltage readings are approximate. The voltage read-
ings “Input to Amplifier” should not be taken with
relay in service.
