DIY Circuit Breaker Current Injection Testing Kit 3

[Imumahdi]

Good Evening gents.
I'm trying to make a makeshift circuit breaker trip testing kit for testing MCCBs that are below 100A, however, due to out of control conditions, I'm stuck with the following:

1- Use a Low voltage switched mode power supply (5v, 500W,100A) and a 1kW 0.05ohms resistor to serve as a load bank so that the power supply giving approx. 100A through one pole of the MCCB under test.

2- Use a 230V/12V 1.5kVA Transformer and connect an appropriately sized resistive load through the MCCB.

I would like to listen to the opinions/insights of experts and discipline practitioners regarding these arrangements and would appreciate any piece on information regarding subject matter.

 

[waross]

I woùld test with AC and test all poles in series.
(Option 2)

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

@ Mr Imumahdi (Electrical)(OP)10 Jul 24 20:48
[COLOR=]"...2- Use a 230V/12V 1.5kVA Transformer and connect an appropriately sized resistive load through the MCCB"[/color].
I have the following suggestion for your consideration.
1. Your option2 is preferred.
2. Suggestion: Add a Variac ahead of the 230V/12V 1.5kVA Transformer. No appropriately sized resistive load through the MCCB is needed. Connect three poles in series.
3. Reference IEC breaker standard for testing method including the conductor size and length etc...
4. Caution: field test values is affected by the site temperature which differs from that of the OEM published TCC (usually as a line). Take note that the TCC is NOT a line but a "band" with different tripping times between "cold" or "hot" state etc..See OEM data for more detail.
Che Kuan Yau (Singapore)

 

[System Protection]

How about a Variac in between your voltage source and the 230V input of the 230/12 transformer?

Then an ammeter on the low side of the 230/12V transformer so you can dial in the current.

 

[waross]

How about a Variac in between your voltage source and the 230V input of the 230/12 transformer?

That's what would do.
Much less costly than a 100 Amp Variac.
I would consider a resistor to limit the maximum current.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

"..Much less costly than a 100 Amp Variac.
I would consider a resistor to limit the maximum current".
1. No. Think over it again. The variac is placed ahead of the 230/12 V transformer, which varies the input voltage to the primary 230 V. It is NOT placed on the secondary 12V circuit.
You neither need a 100A variac nor a 100A adjustable resistor.
2. Reference commercial primary injection test sets on the market. None of them uses 100A variac or 100A resistor.
3. BTW: to test <100 A breakers may need a current of say 500-600 A for say 10-20 minutes. The 230/12 V transformer may requires force fan cooling, activated by a thermostat.
Che Kuan Yau (Singapore)

 

[waross]

I apologize Mr Che.
I misread your post;
" Add a Variac ahead of the 230V/12V 1.5kVA"
I mistakenly saw;
" Add a Variac instead of the 230V/12V 1.5kVA"
Good idea.
My bad.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

@ Mr Imumahdi (Electrical)(OP)
I wish to submit the following additional information for your consideration.
1. Most commercial test sets on the market include a timer, with start/stop by NO/NC dry contact.
2. As a "makeshift", a low cost practical DIY assembly, a variac + 230/12V trafo + a clamp on A meter would be fine. Any readings with 1-2s difference out of minutes makes no difference.
3. However, to measure instant tripping time would need an electronic timer that would be able to read 0.001s. This timer can be added as an additional device if there is a need, otherwise ignore it.
Che Kuan Yau (Singapore)

 

[waross]

100 Amp breakers instantaneous trip?
Instantaneous trips are typically in the range of 5 to 10 times the breaker rating.
If your test set cannot develop 500 Amps to 1000 Amps forget instantaneous trips.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Imumahdi]

@che12345 Your suggestion to add a variac at the input side is very valuable as it saves me the cost of high wattage resistors and their generated heat and gives me the ability to have some control of the output.
Also, for the IEC Standards regarding Circuit breakers test, may I burden you to direct me at which standard to utilize for this matter? I know a simple google search will send me straight to the point but pardon me this time.

As for tripping time analysis, I'm only required to verify the thermal protection function of the circuit breaker at 125% of rated current.

 

[Imumahdi]

@waross You are correct, Sir. But as of now, I'm only verifying the thermal protection functionality of the MCCBs.

Are there any cons to testing with DC? Just asking for my information.

 

[davidbeach]

Do the breakers even have a DC rating? If not, then testing with DC could be a bad idea.

When one this sentence into the German to translate wanted, would one the fact exploit, that the word order and the punctuation already with the German conventions agree.

-- Douglas Hofstadter, Jan 1982

 

[che12345]

Imumahdi (Electrical)(OP)11 Jul 24 18:57
"...for the IEC Standards regarding Circuit breakers test, may I burden you to direct me at which standard to utilize for this matter? ...As for tripping time analysis, I'm only required to verify the thermal protection function of the circuit breaker at 125% of rated current..."
I have the following information for your consideration.
1. Information: In the IEC world, there are two separate/different standards of LV breaker viz. the MCB and MCCB.
a) for MCB, reference IEC 60898,
b) for MCCB, reference IEC 60947-1 series ...
2. Attention: Field test at 125% of rated current only verifies that NO tripping for hours. Reference OEM TCC tripping "band" either cold or hot.
3. If it is used as a "breaker" instead of a switch, it would be more informative to test it at 200% or more to be meaningful.
Che Kuan Yau (Singapore)

 

[che12345]

Imumahdi (Electrical)(OP)11 Jul 24 18:57
"...As for tripping time analysis, I'm only required to verify the thermal protection function of the circuit breaker at 125% of rated current..."
I have the following opinion for your consideration. I may have not understood the circumstance/issue that you are facing, that called for field testing.
1. Usually field test is carried out to verify that the breaker trips when subjected to over-current (overload or short-circuit) within a certain time. This is to ensure that it protects the conductor and the load (which may have another protection). The test current is usually > 1.5 time the current setting. This is to ensure that it DOES trip (within a certain time).
2. It is NOT informative/meaning full to test it at 1.25 time of current setting, which verify that it does NOT trip after say tens of minutes.
3. Why test? The purpose is to verify that as a "breaker" , it Does trip when subjected to over current. A "switch" is to maintain closed under any over-current.
Che Kuan Yau (Singapore)

 

[waross]

2. It is NOT informative/meaning full to test it at 1.25 time of current setting, which verify that it does NOT trip after say tens of minutes.

Unless a breaker is tripping unexpectedly.
Is this a load problem or is the breaker going "soft" and tripping at lower than expected current levels.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

@ Mr Imumahdi (Electrical)(OP)11 Jul 24 18:57
"...As for tripping time analysis, I'm only required to verify the thermal protection function of the circuit breaker at 125% of rated current..."
I hope the problem is solved. I have the following addition information for your consideration.
For MCB
1. when tested with slow increase from 0 to 1.25 rated current (Ir), it does NOT trip say < 5000s. But it trips instantly when switch on at 1.25 times Ir, on certain loads. Why ?
2. the magnetic tripping characteristics are (B 3-5Ir), (C 5-10Ir), (D 10-20Ir) etc..
For a breaker with B tripping characteristic would trip instantly , if the switch on first current peck > 5Ir. This happens on battery charger, and any capacitive loads etc...
3. Propose solution: replace the MCB from B to C (5-10Ir) or D (10-20Ir).
Attention: Do NOT increase the Ir current rating. Change B to C... only change the magnetic instant tripping Ir level, NOT the thermal (over load) tripping time.
Che Kuan Yau (Singapore)

 

[waross]

Many Breaker trips:
Many breakers have two tripping elements.
A thermal trip, works on the heating effect of a current through a small series resistance.
This heat acts on a bi-metal strip to trip the breaker.
The thermal trip has an inverse time characteristic and typically trips at a small percentage of current above the breaker rating.
Thermal trips are used to protect against overloads.
Magnetic trips are often used.Magnetic trips are used for short circuit and fault protection.
Magnetic trips trip instantly.
Magnetic trips typically trip at several times the rated current.
A common tripping range is 5 times to 10 times the breaker rating.
Many breakers have both thermal and magnetic trips.
The combination of thermal and magnetic trips allows a breaker to energize a load that has an inrush current on energization.
When testing with various loads, if the inrush current of a load is greater than the instantaneous or magnetic trip point, the breaker will trip instantly.
Transformer and motors are two examples of loads with high inrush currents.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Parchie]

Y'all.
The power draw should be the amount of power required when connecting the equipment under test plus the test lead resistance plus the load resistance.
E.g. a 100A thermal overload relay with have a resistance per pole of about 0.378 milli-ohms, Using a 38 mm2 x 1 meter cable with a resistance of 0.16 ohms per 1000 feet -> when all those items are connected in series (3 poles of TOR plus two-1 meter test lead plus load bank) will result into a total resistance of 0.05218 ohms! The power capacity required should only be 522 Watts at a voltage of 5.2 volts.