Primary Current Injection instantenous Pickup

[anonymous]

This will be the death of all my specialty terminal connectors and bussing I have collected for primary injection testing if I am understanding correctly.

Inverse time means LT, not INST. Instantaneous is definite time (with partial exceptions for fancier trip units). NEMA is saying to test the long time delay at 3 x LTPU, with the LTD dial at either the highest setting or the specified setting (we always do the coordination study setting in my experience). This clause does not apply to instantaneous pickup tests. Instantaneous tests will be a pulsed ramp to the minimum pickup.

[AaronCBI]

Inverse time means LT, not INST. Instantaneous is definite time (with partial exceptions for fancier trip units). NEMA is saying to test the long time delay at 3 x LTPU, with the LTD dial at either the highest setting or the specified setting (we always do the coordination study setting in my experience). This clause does not apply to instantaneous pickup tests. Instantaneous tests will be a pulsed ramp to the minimum pickup.

Yes exactly.
My specialty circular connectors for RL type breakers will be melted doing maximum time on a 4000 A breaker at maximum delay setting.
Or SACE breakers. The longest setting on those with some of the electronic trips are 144s @ 6x I believe, and they come up to 5000A

[Kalbi_Rob]

Inverse time means LT, not INST. Instantaneous is definite time (with partial exceptions for fancier trip units). NEMA is saying to test the long time delay at 3 x LTPU, with the LTD dial at either the highest setting or the specified setting (we always do the coordination study setting in my experience). This clause does not apply to instantaneous pickup tests. Instantaneous tests will be a pulsed ramp to the minimum pickup.

You are correct, Inverse time means LT, not INST.

You are incorrect on how to perform Instantaneous test in accordance with NEMA AB4:

6.6.4.2.2 Apply a pulse of current, approximately 5 to 10 cycles in duration, and at a level approximately 5%
below the lower tolerance limit specified in Table 4 for the breaker setting. The breaker should not trip.
6.6.4.2.3 Apply a pulse of current, approximately 5 to 10 cycles in duration and at a level equivalent to the
high tolerance limit specified in Table 4. The breaker should trip.

What you are describing is similar to the Ramp up test, but not the same as NEMA calls for ramping current at a rate of 2-5 sec, which has been proven to damage rheostats on many test machines.

[anonymous]

Yes exactly.
My specialty circular connectors for RL type breakers will be melted doing maximum time on a 4000 A breaker at maximum delay setting.
Or SACE breakers. The longest setting on those with some of the electronic trips are 144s @ 6x I believe, and they come up to 5000A

Totally misunderstood you. I have no experience with RL breakers but we did do some SACE breakers last year with one of these adjustable stab sets, which worked great: http://www.newengland-tool.com/id22.html. But they were 3200A and the time dial was not all the way up. At 144s and 5000A the LTD test would be 15000A for about 2.5 minutes! That is some serious current and a PI-6000 would have trouble pushing that according to the spec sheet (max on time for 18kA @ 9V = 1.5 mins).

You are correct, Inverse time means LT, not INST.

You are incorrect on how to perform Instantaneous test in accordance with NEMA AB4:

6.6.4.2.2 Apply a pulse of current, approximately 5 to 10 cycles in duration, and at a level approximately 5%
below the lower tolerance limit specified in Table 4 for the breaker setting. The breaker should not trip.
6.6.4.2.3 Apply a pulse of current, approximately 5 to 10 cycles in duration and at a level equivalent to the
high tolerance limit specified in Table 4. The breaker should trip.

What you are describing is similar to the Ramp up test, but not the same as NEMA calls for ramping current at a rate of 2-5 sec, which has been proven to damage rheostats on many test machines.

I did not know that! I was taught to start just below the low tolerance, then inject higher and higher until the breaker trips, and then the trip current is the test result. What you/NEMA says makes sense, it's similar to how we test relays where they want to prove both sides of a tolerance. Thanks for the info, I guess I need to read the NEMA book some more.

[Kalbi_Rob]

Totally misunderstood you. I have no experience with RL breakers but we did do some SACE breakers last year with one of these adjustable stab sets, which worked great: http://www.newengland-tool.com/id22.html. But they were 3200A and the time dial was not all the way up. At 144s and 5000A the LTD test would be 15000A for about 2.5 minutes! That is some serious current and a PI-6000 would have trouble pushing that according to the spec sheet (max on time for 18kA @ 9V = 1.5 mins).



I did not know that! I was taught to start just below the low tolerance, then inject higher and higher until the breaker trips, and then the trip current is the test result. What you/NEMA says makes sense, it's similar to how we test relays where they want to prove both sides of a tolerance. Thanks for the info, I guess I need to read the NEMA book some more.

I personally have never met anybody test it per NEMA (nor would I test LT delay at max) in the 3 separate companies I have worked for, but I got into an argument with Siemens engineer rep over how to test. The Instantaneous failed to trip all the way up to 10x when set to 5x. He told the customer, Siemens would not validate the test results (for warranty replacement) since they were not performed 100% per NEMA AB4, and they would have to test it at their facility to verify operation.
Needless to say, this same Siemens engineer rep, gave me issues on another project when they had multiple breakers failing due to failed power supplies. He tried to convince the customer that my Withstand test on the Switchboard caused his 24Vdc power supply to fail through a open switch, pulled fuses, PT, and DC converter.

[RabbleRabble]

Minor point for educational purposes:
CT's can be used both ways, to decrease current and to increase current (but normally only for decreasing current). They are normally used for metering as you say, but also very often, like in the above example for circuit protection.

Some primary injection test sets like the SMC raptor uses a large CT to increase current. You run the heavy current cable through the hole and the system produces several thousand amps from a relatively small current (and higher voltage). You can also gang several of them together to further increase the current.
https://www.protecequip.com/products...testing-system

Thanks I’ve never seen that before. I wonder how the primary current is measured?