Technical Guide
Testing self-powered relays with SVERKER 900
Page 19(33)
5.2.5. Can we accept the test results?
SVERKER 900 is a relay test equipment that lets the engineer decide if the test result is Ok or not.
From the graph shown in Figure 22, the result is doubtful: a noticeable
large deviation from the “theoretical
curve” is noticed.
As a rule of thumb (due to the voltage level where these relays are requested to operate) if the measured points
are within 10% (or 15%) of the theoretical characteristic, the test results can be accepted without need of
deeper investigations. The combination of relay error and CT error
11
can justify this approach.
One error in the current measurement, is reflected as an error on the operate time. To easily verify this
graphically with a reasonable approximation (valid for small percentages of errors: 10% is a small percentage),
it is possible to draw the characteristic with new modified settings: 10% above and 10% below the real settings.
In this case, we obtain two curves that reasonably show the error in the time characteristic.
When the error for the measured current is below the injected value, we obtain the characteristic with times
above the theoretical times. When the error is above the injected value, we obtain the characteristic below the
theoretical one.
The characteristics that will be drawn are then:
CURVE “BELOW” (Figure 23):
I>_test= 0,6 A * 0,9 = 0,54 A
Char
acteristic Normal Inverse (IEC “A”: Inverse, par. 4.1.1)
Time Multiplier (a) =0,3
I>>_test = 4,0 A * 0,9 = 3,6 A
Characteristic Definite Time
Time Delay t = 200 ms
Figure 23. Graphical verification for the time curve for measurement errors 10% higher than the injected ones.
These measured points are above the curve
“BELOW”.
CURVE “ABOVE” (Figure 24):
I>_test= 0,6 A * 1,1 = 0,66 A;
Char
acteristic Normal Inverse (IEC “A”: Inverse, par. 4.1.1)
Time Multiplier (a) =0,3
I>>_test = 4,0 A * 1,1 = 4,4 A
Characteristic Definite Time
Time Delay t = 200 ms
11 consider that we are injecting the currents from a small winding, and through the real secondary winding it reaches the
analog inputs of the relay
