Undervoltage protection setup

ifconfig

First off, I am a householder and not an electrician so this is in reference to some protection I have put in with recommendation from a heating engineer and installed by my electrician.

So , the back story is that I have a Ground source heat pump in since 2007 installed in our separate garage building.
Supply is single phase with enhanced supply (16kVA , I believe - with our own transformer on the supply beyond the boundary of our garden, rural Mayo.

Over the years on over 3 occasions I have had to replace the soft start module on the heat pump (and occasionally a capacitor as well). Our heating engineer who services the heat pump strongly suspected that the soft start fried out due to brownouts or undervoltage.

I generally noticed this to happen in or around the time of winter storms when the heat pump would have been calling for heat more and we suspect various loads on the grid and potentially wind sway (not necessarily on our site but along the line) may have led to the supply voltage being below normal tolerance during period of heat pump operation. The soft start module is rated at 32Amperes. I did have ESB networks supply one of those recorders in the house 5+yrs ago but it was during finer weather and they determined that my supply showed no anomalies that would be outside the EU regulations,etc.


So, in order to at least provide some level of protection for the sensitive electronics in the HP , I was told about single phase voltage threshold relay which (in combo with a contactor) would provide some level of protection if the supply dipped below (or above) certain limits. It's a neat unit which provides min/max thresholds for the single phase voltage supply as well as a time control which prevents nuisance tripping. The unit doesn't shut off like a circuit breaker, it opens the contactor, I believe and restores it to closed once the voltage supply conditions correct themselves.

That has been in for a while and certainly the HP has worked away and no burn outs of the soft start in the HP.
The one thing that I have noticed is that there is a very noticeable light flicker (particularly on the less energy efficient bulbs) in the house each time the HP starts. The soft start module is supposed to smooth that out and I believe it did in the original configuration.

What I am wondering is, if it even makes sense that the undervoltage protection I have had installed could be nuisance tripping somehow each time the heat pump starting current happens and the ride through where the relay resets might be causing the contactor to very briefly open and shut (and arc a bit) ?
I am probably massively overthinking but the blinking of the house lights jars with me a bit.
It's not just one lighting circuit in the house. I've seen the lights to dip both upstairs and downstairs and I have 100% correlated it to the heat pump starting.

My electrician set the threshold relay to 210V as the low voltage threshold and 5 seconds as the time param to avoid nuisance tripping.

Any perspectives welcome.

Lenar3556

I would be interested to know why the heating engineer believed under voltage to be the root cause of the inverter failure. Why not over voltage? Or some other power quality issue? Or a weakness in the design of the soft start?

Is this soft start part of the heat pump itself?

207-253VAC is considered an acceptable voltage range in Ireland and most of Europe. Although the fact you have your own transformer, presumably fed with 10/20kv should provide you with an above average quality of supply.

The under/over voltage detection relay is certainly no harm to have, but I would be surprised if you have voltage problems, unless this is specifically indicated.

It is also most unlikely that the voltage detection relay is the cause of dimming / flickering lights. If this is significant, and/or a new issue it should be investigated by your electrical contractor initially. There could be a poor connection at some point in the supply to the house, or issue at the transformer.

Have you been having any equipment failures otherwise in the house which were out of the ordinary?

ifconfig

Thanks Lenar.

Regarding under-voltage being speculated by my heat pump maintenance guy...
The explanation he has given is that (from memory) with these inductive motors/compressors there is a high instantanous starting current required as opposed to the running of the compressor.
The soft start module should be overengineered but I know that it is rated at 32Amps.
It is integrated into the heat pump.
On at least 3 occasions I've had to get him back to replace the soft start module (unit has been in since 2007).
It is hard to determine the exact fault path but it seemed to me that it happened typically on extremely stormy nights.
There was over current in the soft start .. he explained that low voltage-> high current .. so I am guessing the unit was in its start phase and the supply voltage was browned out and the combo of say < 207VAC and the draw from the heatpump may have brought the softstart above its 32A rating ??

And as for the current dimming , it is 100% correlated to the heat pump starting.
Our installation probably would have benefitted from a larger buffer tank inside the house, because we do get a fair bit of cycling of the heat pump so the HP would typically kick in (I am guessing) > 100 times a day on a cold day.
However, the soft start in the HP certainly did its job of not causing lights to appreciably dim/flicker.
The only new change now is the insertion of the protective circuitry with the voltage protection monitor/relay and the contactor (rated 63A).

The cables from the transformer at back of garden (large site) are buried underground.
The electrician measured stuff at the main house circuit breaker and didn't see anything unusual when I called him out while this dimming was happening fairly recently.
The HP guy did mention about recommending someone do an inductance test for the various runs of supply to the house , I believe, just to rule that out.
What I was wondering was if the HP start itself was bringing the voltage below 210V briefly and enough to feedback and trigger the relay to auto-restart and cause the contactor to disengage and re-engage after each HP start sequence.

My electrician doubts that as he reckons the HP itself would be knocked out and reset in such a way that the whole unit would go dark on its LED/control panel.

2011

ifconfig wrote: »

The explanation he has given is that (from memory) with these inductive motors/compressors there is a high instantanous starting current required as opposed to the running of the compressor.

This is true. Motors such as this have a high starting current.

Very roughly (and mostly accurate):

When power is applied to the motor it is essentially a short circuit for a brief time. As the motor starts to turn it generates a "back emf". This is results in an opposing current that results in a net decrease in the current drawn.

The soft start module should be overengineered but I know that it is rated at 32Amps.

The soft starter should be sized for the motor, this is not "over engineering".

A soft starter reduces the starting current. It achieves this by applying a reduced voltage during start up and slowly ramping it up. This ramping up should occur as the motor speed ramps up (if all is going well).

There was over current in the soft start

This could happen if the soft start applied a higher voltage than was suited ot the speed of the motor. This can happen if the mechanical load on a motor is too high.

Very roughly:

Higher voltage = higher current (with everything else being equal)

Higher current = higher torque. This is why these motors have so much torque at low speeds.

Higher speed = higher back emf = reduced current drawn from the supply (with everything else being equal)

Increased mechanical load = lower speed = higher current (with everything else being equal)

So why would mechanical load increase?
- Bearing issue
- Rotor can not turn freely
- Other

And as for the current dimming , it is 100% correlated to the heat pump starting

Volt drop is proportional to the current. So I would expect this when there is a dramatic load change which is what you are describing. I can't say if your is excessive or not.

I would look at:
1) Reducing the frequency of stop / starts of the motor. These stress the system.

2) Using a high quality soft starter such as ABB. Soft starters are crude units that "chop" the waveform to reduce the applied voltage. They are not like inverters / VSDs which are far superior.

3) Best of all would be a VSD that converts single phase to 3 phase connected to a 3 phase motor. Not cheap but they can do things such as running in constant torque mode so that the applied current can be kept within defined limits.

4) Can the soft starter be adjusted to ramp up more slowly?

ifconfig

I did read a discussion regarding a different manufacturer's heat pump (NIBE , also popular in Ireland) whereby someone had issue with Soft start failing and some discussion was made about whether such HPs should be designed to use a soft start or should use inverter/3 phase. It kind of goes above my head in some places but here is the discussion

http://www.ultimatehandyman.co.uk/forum1/viewtopic.php?t=83672

So, I do realise that soft start modules can fail on these configurations. My solution based on some advice was to get the voltage threshold relay + contactor in front of the heat pump , since the soft start modules are typically 300Euro + or so and with call out and labour costs not shy of 500Euro.

My bigger concern now is just the appearance of the light dimming. I think the only way I can reduce the frequency of heat pump starts is the plumbing inside a house and having a larger receiving buffer tank for the underfloor heating. But I do agree having more restarts does put more stress on the system.

With the light dimming - too much knowledge is a dangerous thing but what comes up a lot is the idea that there may be a faulty neutral. The electrician did check connections at the main circuit breaker and found nothing. However, when does it become prudent to call out electrical supplier to check transformer and the supply to the house say as far as the meter, etc.

Are there further checks that I can ask my electrician to carry out before going that far. I am not sure if he measured stuff while the dimming was happening - I've since correlated that dimming to the start of the heatpump. Someone mentioned an impedance test for the various runs into the house, out to garage , back to transformer.

The lights didn't dim as noticeably say 1 yr ago. The soft start component is meant to address that and the new one is in < 1 yr. So, I'd just want to eliminate that there is a dodgy neutral issue for peace of mind.

2011

ifconfig wrote: »

I did read a discussion regarding a different manufacturer's heat pump (NIBE , also popular in Ireland) whereby someone had issue with Soft start failing and some discussion was made about whether such HPs should be designed to use a soft start or should use inverter/3 phase. It kind of goes above my head in some places but here is the discussion

3 phase is always superior.
VSDs offer a lot more options but obviously there is a substantial cost implication.

So, I do realise that soft start modules can fail on these configurations.

A quality soft starter, properly selected and installed should not fail.

My solution based on some advice was to get the voltage threshold relay + contactor in front of the heat pump

You need to consider that the starting of the motor causes a volt drop. How will your proposal fix this? You may just disconnect the motor every time it attempts to start (as this is when the largest volt drop will occur).

The idea of the soft starter is to reduce the inrush (or starting) current. If you implement this you will need to ensure that the soft starter is used to restart the motor following the reconnection.
How do you intend on achieving this?

I think the only way I can reduce the frequency of heat pump starts is the plumbing inside a house and having a larger receiving buffer tank for the underfloor heating.

Or change the control wiring so that you have more hysteresis.

With the light dimming - too much knowledge is a dangerous thing but what comes up a lot is the idea that there may be a faulty neutral.

A "faulty" neutral suggests a poor connection on the neutral. This may cause dimming of lights alright. Equally so would a "faulty" connection of the phase conductor (live).

I suspect there is no "fault". When there is a step change in the load applied to a transformer this will result in a volt drop, this can manifest itself in the way you describe.
It is possible that the volt drop is excessive and this may be due to a number of reasons such as an undersized transformer or undersized cabling.

The electrician did check connections at the main circuit breaker and found nothing.

Not a lot to find other than a poor connection or an undersized cable (which the electrician may not like to highlight).

However, when does it become prudent to call out electrical supplier to check transformer and the supply to the house say as far as the meter, etc.

Yes, especially the transformer. This is a common problem, you are not alone.

Are there further checks that I can ask my electrician to carry out before going that far.

What size is the transformer? Are there other loads connected to it? How far is it from the house? What other large electrical loads are there (instantaneous shower, ovens, hob, immersions)?

I've since correlated that dimming to the start of the heatpump.

Yes, taht is exactly what I woudl expect.

Someone mentioned an impedance test for the various runs into the house, out to garage , back to transformer.

I think they mean a resistance test. High resistance joints / cabling / condcutors would increase the volt drop. They may be confusing it with an earth fault loop impedance test.

ifconfig

Many thanks for the very useful answers and explanations of possible causes.

One thing I am wondering is, whether there is some etiquette or protocol regarding contacting ESBN to come out and check the transformer and connections as far as the meter box ?

Do they insist that your electrician has first done some preliminary checking or can a customer contact them directly with concerns.

In one of the posts it was mentioned that the electrician may or may not want to highlight potential issues with supply.
That's not the first time I heard of that.
I think I remember one of the tradesmen (possibly heat pump maintenance guy) saying that not all electricians would want to get involved (say in resistance, ground/impedance testing, etc).

So, do I have grounds to contact ESBN directly just to rule out supply (eg distance of transformer pole to house and cabling) or should this all involve my electrican (who is a good guy, no complaints).