Testing more complicated elements that use a percentage or ratio between values can be difficult if you cannot properly define all of the values in the equation. It doesn’t help that different people can define the same element using different terms, especially when they don;t define their terms in their documentation.
We were attempting to test a Basler BE1-47N negative Sequence Voltage relay. This relay measure the percentage of negative sequence voltage in a system. Negative sequence is universal [V2 = (Va + a2Vb + aVc)/3], but our test set used the formula %V2=100 x V2/V1 and the results were OK when the pickup setting was very small. As the pickup grew, the percent error between expected and actual test results increased. We could not find the formula in the manual and tech support at Basler was unable to help us either.
We figured out that the relay uses the formula %V2=100 x V2/V1nom. The relay’s nominal voltage was 120V P-P which would be 69.28V P-N.
V1 gets smaller when V2 increases, so the difference between the test-set V2% and the relay’s V2% grew as more V2 was applied.
Always know how the relay and your test-set calculate values so that you can compare apples to apples!
