Instruction Leaflet
All possible contingencies which may arise during installation, operation or maintenance, and all details and
variations of this equipment do not purport to be covered by these instructions. If further information is desired
by purchaser regarding this particular installation, operation or maintenance of this equipment, the local ABB
Power T&D Company Inc. representative should be contacted.
CAUTION
!
Before putting relays into service, operate the
relay to check the electrical connections.
Close red handle switch last when placing
relay in service. Open red handle switch first
when removing relay from service.
1. APPLICATION
The SA-1 relay is a three-phase high-speed relay
used for differential protection of ac generators and
motors. With proper selection of current transformers,
the relay is unaffected by dc transients associated
with asymmetrical through short-circuit conditions.
Current transformer burden in ohms should not
exceed (N
P
V
CL
)/133; further, the burden factor, BF,
should not differ by more than a 2 to 1 ratio between
the two sets of ct’s. The above terms are defined as:
N
P
=
proportion of total number of ct turns in
use
V
CL
=
current transformer relaying accuracy
class voltage (e.g. C400, V
CL
= 400)
B
F
=
R
B
=
resistance of the burden, excluding ct
winding resistance
In calculating the burden, use the longest one-way
lead resistance from the ct to the SA-1 for distribution
transformer or resistance grounded machines. Use
twice the longest one-way lead resistance for reac-
tance grounded machines.
For example, if the 400/5 tap of a 600/5 multi-ratio ct
is used, N
P
= 400/600 = 0.67. If this ct has a C200
rating, V
CL
= 200, and the burden should not exceed:
Assuming a resistance burden of R
B
= 0.5 ohms, the
burden factor, BF is:
The other set of ct’s may than have a burden factor
as high as 2 x 3.8 = 7.6, or as low as 1/2 x 3.8 = 1.9.
If the other set of ct’s also has a burden of 0.5 ohm, a
C100, C200, or C400 rating would be satisfactory
since the burden factors are 7.6, 3.8 and 1.9 respec-
tively.
2. CONSTRUCTION
The type SA-1 relay consists of a Restraint Circuit,
Operating Circuit, Sensing Circuit, Amplifier Circuit,
Trip Circuit, Indicating Circuit, Surge Protection Cir-
cuit and external reactors. The principal parts of the
relay and their location are shown in Figures 1
through 8.
1000
R
B
N
P
V
CL
----------------------
N
P
V
CL
133
--------------------
0.67
200
×
133
----------------------------
1.0 ohm
=
=
BF
1000
R
B
N
P
V
CL
---------------------
1000
0.5
×
0.67
200
×
----------------------------
3.8
=
=
=
Type SA-1
Generator Differential Relay
Supersedes I.L. I.L. 41-348.1G, Dated January 1985
( | ) Denotes Change Since Previous Issue
Effective:
November 1997
41-348.1H
ABB Automation, Inc.
Substation Automation & Protection Division
Coral Springs, FL
Allentown, PA
