×
Follow Us
Results 1 to 4 of 4

long time delay primary injection testing

 Jump to latest post
    #1
  1. KLLU26 is offline Junior Member Pro Subscriber
    Join Date
    Oct 2018
    Posts
    5
    Reputation

    long time delay primary injection testing

    i've been testing for about 4 months now and one question i seem to keep asking (and haven't gotten a definitive answer) pertains to the recorded times of the long time delay during primary injection testing of a molded case square d circuit breaker.

    while testing A phase, at X current we would record roughly 60 seconds.

    B phase would drop to around 35-40 seconds,

    C phase would be similar.

    now i am familiar with the fact that as the breaker heats up the trip time will decrease, so my question is about the value that we record. in my mind under a normal load the breaker will be warmer, obviously, so during an overload the breaker would most likely trip around the 35-40 second mark. so why would we record and expect our values to be around 60 seconds from a cold test? i think it would be more accurate to record and expect the 35-40 second reading in a real world situation.

    is this just part of the manufacturers specification or NETA standards?

  2. #2
  3. Join Date
    Jun 2016
    Location
    Boston, Ma
    Posts
    2
    Reputation

    SQ D Instructions

    This SQ D IB gives you some reference specifically page 14.
    SQ D Field Test and Maint 0600IB1201 2013.pdf
    Quote Originally Posted by KLLU26 View Post
    i've been testing for about 4 months now and one question i seem to keep asking (and haven't gotten a definitive answer) pertains to the recorded times of the long time delay during primary injection testing of a molded case square d circuit breaker.

    while testing A phase, at X current we would record roughly 60 seconds.

    B phase would drop to around 35-40 seconds,

    C phase would be similar.

    now i am familiar with the fact that as the breaker heats up the trip time will decrease, so my question is about the value that we record. in my mind under a normal load the breaker will be warmer, obviously, so during an overload the breaker would most likely trip around the 35-40 second mark. so why would we record and expect our values to be around 60 seconds from a cold test? i think it would be more accurate to record and expect the 35-40 second reading in a real world situation.

    is this just part of the manufacturers specification or NETA standards?

  4. #3
  5. gchoquette is offline Junior Member Pro Subscriber
    Join Date
    Mar 2019
    Posts
    22
    Reputation

    The test is performed at a standard temperature for repeatability reasons.

    Quote Originally Posted by johnierw View Post
    This SQ D IB gives you some reference specifically page 14.
    SQ D Field Test and Maint 0600IB1201 2013.pdf
    From the reference above:
    "Trip times are measured from a “cold start.” A cold start, as defined by Underwriters Laboratories Inc. Standard 489 occurs at 25°C ± 3° (77°F ± 5°). Therefore, before beginning overcurrent testing, the circuit breaker must be in 25°C (77°F) ambient temperature long enough for all parts to reach that temperature. Circuit breakers that have been in higher ambient temperatures may take two to four hours to reach the steady state temperatures mentioned above."

    The problem with testing a circuit breaker warm of even hot, is that the trip time values cannot be referenced to a standard value because we don't know how "warm" is warm. That's why we test at 25C or 77F.

    Ideally, there could be a table of trip times as a function of CB temperature, but that would be difficult to measure accurately and it would drop during the test.

  6. #4
  7. CEBrighton is offline Junior Member Pro Subscriber
    Join Date
    Feb 2019
    Posts
    3
    Reputation

    Thermal memory

    What your experiencing is thermal memory. (Thermal imaging effect) Typically it explains this in the manual and lets you know what time that specific breaker needs to reset. The ones we have been testing lately have been 20 min.

Subscribe

Share this thread

Related Topics

  1. How long I should wait before attempting the NETA Level 4?
    By JohnRaz in forum NETA Level 4 Exam
    Replies: 7
    Last Post: March 19, 2022, 12:54 PM
  2. Primary Current Injection Test
    By changeabilities in forum Electrical Testing Talk
    Replies: 4
    Last Post: August 12, 2018, 08:17 AM
  3. Primary current injection 138kV breaker with bushing CT's
    By david2458 in forum Electrical Testing Talk
    Replies: 1
    Last Post: April 12, 2018, 05:27 AM
  4. High Current Injection LTD Test Value
    By alexlounsbury in forum NETA Level 3 Exam
    Replies: 5
    Last Post: July 10, 2017, 11:38 AM

Tags for this Thread

Follow us


Explore TestGuy


NETA Certification Training


NICET Electrical Power Testing


Help and Support




You are viewing the archives. Enjoy new features and join the conversation at wiki.testguy.net