3 Phase Electric Question

[wolfmanjack]

Like every one in Thailand i have problems with the "brown outs". My problem is that my thai workers keep using my 3 phase machines when the power is too low and it burns out my motors. At least that is what I think is happening. My head worker called a thai electrician to check it out and they are telling me i need to replace all of my wiring, my breaker box and all of the breakers. For the life of me I can not see how that is going to solve the problem. Am I being stupid or would replacing all of this actually accomplish anything besides making me spend a bunch of money?

The only solution that can think of is if there was a device similar to a breaker that would shut down the line if the power level dropped too low. Does such a beast exist ??

Any other suggestions to solve this problem ?

[verydumbubba]

Short answer is a decent local, diesel standby genset. Dont rewire squat.

Check peak load times, ban heavy use then.

Bubba

[thaimite]

Like every one in Thailand i have problems with the "brown outs". My problem is that my thai workers keep using my 3 phase machines when the power is too low and it burns out my motors. At least that is what I think is happening. My head worker called a thai electrician to check it out and they are telling me i need to replace all of my wiring, my breaker box and all of the breakers. For the life of me I can not see how that is going to solve the problem. Am I being stupid or would replacing all of this actually accomplish anything besides making me spend a bunch of money?

The only solution that can think of is if there was a device similar to a breaker that would shut down the line if the power level dropped too low. Does such a beast exist ??

Any other suggestions to solve this problem ?

Yes there are three phase protection relays specially designed for such events. This link is a sample of a unit available in Bangkok. http://tinyurl.com/n24gyb

The actual device you require will depend on motor size and other factors and you will need a skilled Industrial electrician to wire it in for you. Do not expect a common "house Spark" to know what he is doing.

If you need more info please PM me

[mackayae]

UVR. Under voltage relay. If your motor has a starter or contactor, you can connect the normally closed auxiliary contact of the UVR in series withe starter or contactor coil. Before you do that, you should check your system voltage at no load and full load. The two readings should be the same. The 3 phase line to line voltage should be 380 volts. Also check the nameplate (motor) voltage, that should also be 380 volts. Also if you always have a low system voltage, you could connect a step-up or boost xfmr on the supply side of the motors.

You should identify the problem first and then come up with a solution.

[Crossy]

You could also get a 3-phase AVR (or stabilizer), obviously if you have big machines this could get expensive (although maybe cheaper than continually replacing motors)

I'll move this to DIY where the sparkies hang out, maybe someone will have a better idea

Would replacing your 3-phase motors with equivalent single-phase units be practical?

[Sojourner]

The question that comes to my mind is how the factory is wired. Is the wiring too small for the devices and is the service coming into the building too small for the full load? On the other hand is the factory at the end of the line and the users up stream are drawing the entire line down in which case the utility company has to up grade. I would contact an electrical engineer/contractor specializing in industrial appliations and have the problem sorted out before spending a lot of money needlessly. A 24 hour voltage recorder on the incoming service would be my first choice to source the problem.

[verydumbubba]

Tnx Crossy - unfortunately, power is like most things in life, you can never be too rich, too skinny, too good-looking.

Same/Same power - it is impossible to make up the deficit without more power, ergo Gensets.

It is a global phenomena.

Bubba

[wolfmanjack]

UVR. Under voltage relay. If your motor has a starter or contactor, you can connect the normally closed auxiliary contact of the UVR in series withe starter or contactor coil. Before you do that, you should check your system voltage at no load and full load. The two readings should be the same. The 3 phase line to line voltage should be 380 volts. Also check the nameplate (motor) voltage, that should also be 380 volts. Also if you always have a low system voltage, you could connect a step-up or boost xfmr on the supply side of the motors.

You should identify the problem first and then come up with a solution.

most of the time we have enough power but sometimes the power drops down and other times the 3 phase drops out. The problem is this happens quite a lot during the rainy season.

I will get someone to check the voltages at no load and full load to make sure it is okay when the power is at full strength.

[Lancelot]

If you lose one phase of the 3 phase line, it will burn out your motors muy pronto. Like another poster suggested, you can get protective devices that can detect when a phase is out and open the circuit to keep your motors safe. If 3 phase protection solves your problem then I doubt the factory need to be rewired.

[wolfmanjack]

Thanks for the input every one. I think I am going to go with the controllers that Thaimite suggested. I am sure I will have to keep an eye on them to make sure the workers do not bypass the controller though.

Any other suggestions are appreciated. Anything I can do to make things run smoother.

[tjo o tjim]

Is it a lot of motors or just a couple?

All you need to do is add a VFD (Variable Frequency Drive). The VFD can be fully single-phased and still drive the motor at three phase. It will usually cost about 1.5x the cost of a motor, but for many applications it can pay for itself in energy savings. It can also provide the protective functions if the voltage drops too low, and can ramp the motor up to speed rather than causing a big inrush current and associated voltage dip.

[elkangorito]

The OP has revealed nothing about the installation. Some of the ideas so far have been very good but until the OP reveals the EXACT conditions of the installation, no difinitive answer can be given.

[wolfmanjack]

Is it a lot of motors or just a couple?

All you need to do is add a VFD (Variable Frequency Drive). The VFD can be fully single-phased and still drive the motor at three phase. It will usually cost about 1.5x the cost of a motor, but for many applications it can pay for itself in energy savings. It can also provide the protective functions if the voltage drops too low, and can ramp the motor up to speed rather than causing a big inrush current and associated voltage dip.

i have quite a few motors but 3 have burned out in the last 2 months.

[wolfmanjack]

The OP has revealed nothing about the installation. Some of the ideas so far have been very good but until the OP reveals the EXACT conditions of the installation, no difinitive answer can be given.

What do you need to know ? I have my own 100 kva transformer and the machines are about 50-60 meters from the transformer.

If any one can give me the number of an industrial electrician in Chiang Mai i will have them out to look and run all of these idea past him.

[Naam]

Like every one in Thailand i have problems with the "brown outs". My problem is that my thai workers keep using my 3 phase machines when the power is too low and it burns out my motors. At least that is what I think is happening. My head worker called a

thai electrician to check it out and they are telling me i need to replace all of my wiring, my breaker box and all of the breakers. = bull!

For the life of me I can not see how that is going to solve the problem. Am I being stupid or would replacing all of this actually accomplish anything besides making me spend a bunch of money?

The only solution that can think of is if there was a device similar to a breaker that would shut down the line if the power level dropped too low. Does such a beast exist ??

Any other suggestions to solve this problem ?

i had one built for my house after spending a fortune replacing relays in aircons and pumps. cost including installation 30k Baht. works perfect! the device shuts down a single phase when its voltage drops 8% (percentage can be adjusted). also no problem to rewire it in order to shut all three phases down when the voltage of only one phase drops which too burns out 3-phase motors.

[david96]

Information on the Electrical Installation would be useful to answer your problem.

Size of consumers mains. in sq mm.

Type of conductor, Al or Cu.

Size of final subcircuits to motors

Size and type of protective devices for cable protection

Size of motors in kilowatts

Route length of circuits in meters from Main Switch board.

Type of motor starting, DOL, Star Delta, etc

.

(Soft starters are now available and are cost effective with other forms of starters.)

Overload and Single Phasing protection settings of individual motor starters.

Phase failure/ phase sequence relays are available with combined under voltage

protection. These will protect individual motors.

A 100Kva transformer can deliver 150 amps per phase at 380/220 volts 50Hz.

It would appear that the problem could be with the supply authority, loss of one phase

of the HV system (eg in the storm season) or heavy loads on the supply transformer atcertain times of the day.

You should install a voltage/ current recorder at the main switch board and this will show

when you have low voltage problems

Edited July 25, 2009 by david96

[tjo o tjim]

You would need to replace all the wiring if everything is simply under-sized. One cheap solution is to have someone read the utility meter every hour on the hour during the day to figure out your average kW demand per hour.

The other "easy" thing you can do is make a list of the motor sizes, and what kind of duty they have: do they start and stop frequently, periodically, or just once a day? If you have more than 80kW of motors, the transformer isn't big enough. If they start and stop across the line frequently and you have about 60kW, then that can cause problems...

Basically, if you want to figure out what the problem is, you need to first determine if it is coming from inside or outside your plant. If your priority is to stop burning out motors, then a VFD is the perfect solution... although it might help you burn down your building if your feeders are overloaded.

[wolfmanjack]

Information on the Electrical Installation would be useful to answer your problem.

Size of consumers mains. in sq mm.

Type of conductor, Al or Cu.

Size of final subcircuits to motors

Size and type of protective devices for cable protection

Size of motors in kilowatts

Route length of circuits in meters from Main Switch board.

Type of motor starting, DOL, Star Delta, etc

.

(Soft starters are now available and are cost effective with other forms of starters.)

Overload and Single Phasing protection settings of individual motor starters.

Phase failure/ phase sequence relays are available with combined under voltage

protection. These will protect individual motors.

A 100Kva transformer can deliver 150 amps per phase at 380/220 volts 50Hz.

It would appear that the problem could be with the supply authority, loss of one phase

of the HV system (eg in the storm season) or heavy loads on the supply transformer atcertain times of the day.

You should install a voltage/ current recorder at the main switch board and this will show

when you have low voltage problems

i am going to have to do a lot of reading to figure out what most of this means in order to know what I have. I know I have 84 hp in total. None of my motors are over 5 hp and most are 3 hp. I will have to look and see if i can read the amps or kw of the motors from the plate on the motor.

[wolfmanjack]

You would need to replace all the wiring if everything is simply under-sized. One cheap solution is to have someone read the utility meter every hour on the hour during the day to figure out your average kW demand per hour.

The other "easy" thing you can do is make a list of the motor sizes, and what kind of duty they have: do they start and stop frequently, periodically, or just once a day? If you have more than 80kW of motors, the transformer isn't big enough. If they start and stop across the line frequently and you have about 60kW, then that can cause problems...

Basically, if you want to figure out what the problem is, you need to first determine if it is coming from inside or outside your plant. If your priority is to stop burning out motors, then a VFD is the perfect solution... although it might help you burn down your building if your feeders are overloaded.

Thanks for the advice. I will have someone do that on Monday. Personally I think the problem is from outside. The spikes and drops are causing the problem. Mostly the drops in power during the rainy season. I can see when the lights dim that the power is too low. One poster suggested diesel generators but there has to be a cheaper solution than that. I sure don't want to burn down my building but i will do some research on the VFD.

[david96]

Contact the PEA.

It appears that the problem could be on the HV side remote from you. Make sure your motor overloads are set correctly to FL motor current for a start.

[elkangorito]

Wolfman, if each & every motor has its own "starter", which it should have, the motor should be protected by a thermal overload (as a minimum). Most high quality thermal overloads incorporate protection against loss of phase.

A standard "motor starter" comprises of;

1] A contactor.

2] A thermal overload.

3] On/Off pushbuttons (pushbuttons are optional).

If you do not have this arrangement, you are in trouble. Every single motor requires "protection" unless you are happy to pay lots of money re-wiring motors or buying new motors.

The thermal overloads should be adjustable. The amperage value of the overload should be 1.25 (125%) of the FLA. FLA means Full Load Current. Example, the motor has an FLA of 10 amps. The overload should be able to be adjusted to 12.5 amps.

The contactors should be AC3 rated for the loading of the motor.

If you don't know about any of these things, good luck finding a Thai "sparky" who does know about this.

One more thing...each & every motor should have its own circuit protection i.e. a circuit breaker. The size of the circuit breaker must be properly coordinated with the "upstream" protection. Not only this, it must be able to properly protect the cable supplying the motor without tripping unnecessarily.

Good luck.

[tjo o tjim]

Elkangorito is right-- proper thermal overloads will protect against a complete single-phasing pretty well. If however you have a single leg that has a lower voltage than the other two (to neutral) that will cause excessive wear on the windings and won't trip the overloads. I see this a lot when you have a three phase service, but put all your single phase equipment off one leg rather than balancing it across all three. This could explain why your sparky wanted to re-wire the place, as the service sounds adequate for your loads.

The simple way to check this is to have the current measured on each of the three legs of the motor. More than a 10% imbalance will cause problems; usually we try to keep it under 3% imbalance. Short-time imbalances up to 10% usually aren't a significant problem unless the motor starts and stops frequently, and they happen at the same time the motor is starting. If this is a problem coming from outside your facility (one of the HV lines also serves all the houses in the area), then we're back at a VFD if you want a long-term solution.

You could potentially put a single VFD for the whole facility, just to provide balanced voltage to your equipment. That isn't usually what anybody would recommend, but if 20-25 or so small VFDs doesn't make sense it could help.

The other problem that you might be having is excessive voltage drop within your place, which could also explain the sparky's desire. Reduced voltage at the motor requires increased current. The motors have full-load rated amps; make sure that you are not exceeding that number as well.

[wolfmanjack]

Okay. It sounds like the controller suggested before might be the best solution then. I just checked the plates on some of my motors and the some are as low as 2 amps. The largest one I could look at was 15 amps. They are all on 30 amp beakers. It sounds like i need to get smaller breakers. Say 5 amp for the 2 amp motor and 20 amp for the 15 amp motor ?

I did not see the point in checking the load today since I just finished an order and only a couple of the machines are running today.

i found a place that sells most of the heavy duty electrical devices on the corner of the airport road and the old lamphun road. i will see if I can get one of their techs to come and take a look. Does anyone know if they are any good or have any other recommendation for industrial electricians in Chiang Mai ??

[wolfmanjack]

Wolfman, if each & every motor has its own "starter", which it should have, the motor should be protected by a thermal overload (as a minimum). Most high quality thermal overloads incorporate protection against loss of phase.

A standard "motor starter" comprises of;

1] A contactor.

2] A thermal overload.

3] On/Off pushbuttons (pushbuttons are optional).

If you do not have this arrangement, you are in trouble. Every single motor requires "protection" unless you are happy to pay lots of money re-wiring motors or buying new motors.

The thermal overloads should be adjustable. The amperage value of the overload should be 1.25 (125%) of the FLA. FLA means Full Load Current. Example, the motor has an FLA of 10 amps. The overload should be able to be adjusted to 12.5 amps.

The contactors should be AC3 rated for the loading of the motor.

If you don't know about any of these things, good luck finding a Thai "sparky" who does know about this.

One more thing...each & every motor should have its own circuit protection i.e. a circuit breaker. The size of the circuit breaker must be properly coordinated with the "upstream" protection. Not only this, it must be able to properly protect the cable supplying the motor without tripping unnecessarily.

Good luck.

It looks like i need to buy starters or do I need them if i buy the 3 phase controllers ? I only have starters on a few machines. many of them are just hooked up directly to a 30 amp breaker.

like I said before I only have this problem in the rainy season when the incoming current frequently drops to what i call a brownout.

[wolfmanjack]

Contact the PEA.

It appears that the problem could be on the HV side remote from you. Make sure your motor overloads are set correctly to FL motor current for a start.

Do you think the PEA would have electricians that would know about all of this advice you guys have been giving ??

[elkangorito]

You could potentially put a single VFD for the whole facility, just to provide balanced voltage to your equipment. That isn't usually what anybody would recommend, but if 20-25 or so small VFDs doesn't make sense it could help.

The other problem that you might be having is excessive voltage drop within your place, which could also explain the sparky's desire. Reduced voltage at the motor requires increased current. The motors have full-load rated amps; make sure that you are not exceeding that number as well.

I must disagree with you tjo o tjim about the bolded part above. I understand your reasoning but at the end of the day, it isn't economically viable for many reasons. I believe that this idea could be discarded.

With regard to voltage variation, there are a few ways around this.

One cheap & simple way is to ensure that the main incoming breaker to the installation has an undervolt coil. In situations of low voltage, the coil would de-energise & open the breaker. I'll give you an example;

The Main Switchboard to my condo is a 2000 amp board. The Main Circuit breaker (2000 amp) was fitted with an undervolt coil & a "detection unit" (Phase Fail Relay). If an undervoltage was detected on any phase, the relay would "drop out" & open the circuit breaker. The purpose of this relay was to protect any 3 phase equipment within the establishment.

One day, I noticed that the power was going on & off every 5 minutes. I went downstairs to investigate. I found that the "maintenance man" had actually discovered that the undervolt relay was burnt out. Instead of beginning a process to replace it, he simply bypassed this function in the Main Circuit breaker. The result is that we get less power interruptions but any 3 phase equipment will most likely be damaged. He didn't seem to understand this concept.

Aside from my condo happenings, the best way to protect expensive equipment in Thailand is to have "Phase Failure Protection" at the Main Circuit Breaker. This will protect all of your equipment. The downside is that the whole installation will be without power if low (or high) voltage is detected.

If you have a low or varying voltage problem, this is a problem for your energy provider to solve. They must solve it free of charge since they have contracted to provide you with reliable electrical energy.

Your average sparky will not know how to deal with this.

Okay. It sounds like the controller suggested before might be the best solution then. I just checked the plates on some of my motors and the some are as low as 2 amps. The largest one I could look at was 15 amps. They are all on 30 amp beakers. It sounds like i need to get smaller breakers. Say 5 amp for the 2 amp motor and 20 amp for the 15 amp motor ?

Be careful. Circuit breakers protect the cables they supply only. Also, there are different kinds of circuit breakers. Eg "fast" acting, "normal" acting & "slow" acting. The slow acting breakers are for things like motors & large transformers. Do not rush out & buy different size breakers unless you know about cable protection, current ratings & circuit breaker types.

Wolfman, if each & every motor has its own "starter", which it should have, the motor should be protected by a thermal overload (as a minimum). Most high quality thermal overloads incorporate protection against loss of phase.

A standard "motor starter" comprises of;

1] A contactor.

2] A thermal overload.

3] On/Off pushbuttons (pushbuttons are optional).

If you do not have this arrangement, you are in trouble. Every single motor requires "protection" unless you are happy to pay lots of money re-wiring motors or buying new motors.

The thermal overloads should be adjustable. The amperage value of the overload should be 1.25 (125%) of the FLA. FLA means Full Load Current. Example, the motor has an FLA of 10 amps. The overload should be able to be adjusted to 12.5 amps.

The contactors should be AC3 rated for the loading of the motor.

If you don't know about any of these things, good luck finding a Thai "sparky" who does know about this.

One more thing...each & every motor should have its own circuit protection i.e. a circuit breaker. The size of the circuit breaker must be properly coordinated with the "upstream" protection. Not only this, it must be able to properly protect the cable supplying the motor without tripping unnecessarily.

Good luck.

It looks like i need to buy starters or do I need them if i buy the 3 phase controllers ? I only have starters on a few machines. many of them are just hooked up directly to a 30 amp breaker.

like I said before I only have this problem in the rainy season when the incoming current frequently drops to what i call a brownout.

If you have a business, it would be very wise to have each individual motor connected to a starter. Each starter should have a contactor & an overload.

[elkangorito]

Sorry...I forgot to mention this.

If your motors;

1] are a few years old or more,

2] have "open" construction (have ventilation holes),

3] have less than "Class F" insulation,

it is not a good idea to connect them to VFD's.