Building Test Loop
Building Test Loop
(OP)
Hi I am with a company based in Idaho called Melni LLC. We make innovative electrical connectors for the industry. Currently we are starting to build our lab to test our connectors in house. I need some assistance on what kind of transformer and other equipment we may need to test properly. We have 480V 3phase power coming from the building. We need to be able to supply a high current load through a loop with the connectors installed to read temperatures at steady states. Depending on the gauge of conductor being used the amperage can vary from around 100 amps up to 1200 amps. Please help me by explaining what kind of transformer is needed and if a variac is used to control the amperage or what kind of equipment I will need to accomplish this task. I know this may seem simple to most of you but I am not an electrical engineer so please take it easy on me.
Thank you,
Thank you,






RE: Building Test Loop
FWIW, we built a high power primary injection set using the core of a large bushing CT from a 275kV transformer, with a primary of heavy cable driven from a 60A variac. The secondary was multiple paralleled lengths of welding cable. The rough & ready calculations are fairly straightforward if you know the load you are trying to drive current through and have some vague idea of the core dimensions. Member scottf will soon tell me that they are pretty damned complicated to do accurately, and he is right. This thing was transportable rather than portable and wasn't something you could use anywhere other than a very tightly controlled environment and lacked even the most basic safety features which you would find on a commercially-available product.
RE: Building Test Loop
Any Thoughts?
RE: Building Test Loop
Do you understand that various meters read Average or RMS and that a rectified current will read very differently depending on which of the two you use?
Are you trying to duplicate the UL test? If so where is the test procedure listing the exact setup and method?
If one of the parties is using AC current and the other is using DC current you will see considerably different results. Are you using different currents?
Any air flow differences will make very large temp reading differences.
Exactly how are you reading the temperature? In this situation the type of measurement tool will make a large difference in readings. If you're using a non-contact method do you realized that shiny verses non-shiny makes an enormous difference in readings?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Building Test Loop
Thank you for your reply,
Yes I understand that the meter may not be reading properly. I am not sure what our meter is reading whether it is average or RMS. It is a Flir CM174. I know that the power source we are using has three phase 480VAC input and produces a rectified DC current.
Yes we are trying to duplicate the test, I have the UL 486A-486B standard which describes the test method and has a figure showing the vertical arrangement of the test specimens. However the standard does not go into detail for whether to test AC vs DC or what to use as a power source etc. It only gives an assigned amp rating based on the conductor size used in the connectors, conductor lengths, TC placement etc.
Yes we are currently using a DC current while they test using AC, we have wondered and asked many times if this would make a difference. We have had a copious amount of people saying no but we still don't understand. Could you please explain how and why this would make a difference in heat rise.
We are testing under controlled conditions.
For temperature measurement we use type J thermocouples with a welded bead tip and a data logger to record the readings.
If you have any more input on this matter it would be greatly appreciated.
Thank you,
RE: Building Test Loop
Watts loss creating heat is described by I2R
Skin effect causes the effective AC resistance to be higher, thus higher I2R losses.
Bill
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"Why not the best?"
Jimmy Carter
RE: Building Test Loop
Also your CM174 is indeed a "true RMS" meter so that's good. It means strange waveforms likely present with any rectification will be correctly measured.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Building Test Loop
As this tests generally takes a long time (hours..) either you have a person continuosly reading the ammeter and correcting manually the variac to keep an steady current output value, or you need to use a constant current electronic device which will keep the current value accurately exact.
This is the only way to get consistent results in thermal tests.
Hope it helps
Eduardo Marchesi
www.smcint.com
RE: Building Test Loop
RE: Building Test Loop
You could use a current controller and a transformer to provide a constant current. A soft-starter that also does current regulation can work for that. We setup a customer with a controller for each phase to drive a transformer for current testing up to something like 3000A and it seems to work OK for them.