Categories

# troubleshooting

#### How to determine the earth fault protection?

##### Saturday, December 19, 2015

Low Voltage (400V-440V) Earthing
This discussion applies to the low voltage side of a (6.5/.400 or 11/.400 or 33/.400 kV transformers). Since your neutral is solidly grounded, the earth fault level will be sufficiently high, to trip the over current (50/51) elements. You will not need any earth fault protection. If you are running long low (really long) voltage cables you may need to provide earth fault protection.

We never design low voltage systems where the ...

#### An Elementary Question About Power Factor

##### Saturday, November 28, 2015

I have an interesting dilemma at work. We have never had the ability to monitor each individual feeder emanating from the substations. I recently installed a modern recloser on one circuit which allows detailed measurement of line characteristics and discovered that we have 1) a serious imbalance among the phases, and 2) a terrible power factor on this feeder - .33 on one phase, and .65 or worse on the other two. The meter that monitors the overall bus reads a combined power factor for the tr ...

##### Wednesday, November 18, 2015

We know the equation kva= kw/power factor. When power factor reduces, kva increases. The substation authorities have to pay a penalty if demand indicator (kva) increases over an integrating period. How the maximum demand (kva) is being calculated in substations. Are there any ways to avoid load shedding of critical loads in substations if the maximum demand indicator goes over a maximum value when power factor is reduced?

In a Tr ...

#### YNyn0 Transformer with Unearthed Primary Neutral

##### Thursday, November 12, 2015

Situation
I have recently encountered a fairly unusual installation where a YNyn0 transformer has been used to supply a low voltage pump installation incorporating a large VFD.
The transformer was initially chosen to offset harmonic distortion with an adjacent Dyn11 supplying an identical VFD.
The transformer has been installed with the primary neutral connection floating in an effort to prevent zero sequence currents from causing nuisance tripping at the su ...

#### Big Submersible Motor/Pump Starting in 5-6 Seconds to Full speed

##### Monday, November 2, 2015

Situation: Here is my current problem and was wondering if anyone had experience of the following:
Application - 260Kw submersible motors/pumps must be running up to full speed within 5-6 seconds of startup.

My proposal had always been to use a soft start until the pump manufacturer has stated that in order to provide sufficient cooling to the stator windings (using the sea water), it must be at full speed in 5-6 seconds.

I have been in touch with ...

#### Why Buchholz Relay Tripped?

##### Monday, October 19, 2015

The Buchholz relays I am used to dealing with have two levels, a Gas Alarm (Volume) and Gas Trip (Surge). They have a nitrogen injection port on the tank side of the Buchholz to inject to test each of these contacts, and a bleed port from the top of the Buchholz which allows for the nitrogen or fault-gasses to be captured for laboratory analysis.

Obviously an open flame is a low-tech way of determining if there are short-chain hydrocarbons present in the gas in the Buchholz, but if ...

#### Why VFD driven motor is hot?

##### Sunday, September 27, 2015

If the induction motor was really hot and you had a premature insulation failure, probably you had an overheating problem. The main reasons for this situation are:

* The voltage waveform created by the variable frequency drive (VFD) has high frequency harmonics that will cause an increase of temperature inside the motor. If your VFD-PWM has no filter outputs and the cable connection VFD-Motor is long, you can easily get a premature insulation ...

#### Electrical Machine Resonance Problems

##### Friday, August 28, 2015

When I at Siemens (my former employer) began building gvpi stators in the 100 mw to 300 mw size, we experienced serious vibration troubles on the end turns both locally in the series connectors and globally in the winding. This was evident in both the 50 Hz and 60 Hz fleets but was more serious in the 50 Hz fleet. This problem led to several forced outages and a few total losses. The problem was that the win ...

#### Why capacitors in VFDs exploded?

##### Sunday, August 2, 2015

I had an oil filled motor start capacitor blow once. What I think happened was when someone replaced it, rather than putting it back in its holder, they duct taped it to the side of the squirrel cage motor that it was starting. They started the motor up and walked away. The motor was a continuous duty motor so it wasn't turned off for a long time. One day, someone shut it off to do some servicing. They notice ...

#### Motor Winding Resistance Unbalance Test

##### Wednesday, July 15, 2015

They were on two different subjects.
(1) Regarding unbalance in winding resistance - If the resistance that if the unbalance in phase resistance is more than 2% the motor has to be rewound.
However, this answer was given assuming the motor is wire wound. However, if it is a motor with formed coils, there exists a possibility that the motor could be partially repaired by detecting the defective coil and repairing/replacing the defective coil.

(2) The other part of the d ...

#### Running motor at 150 Hz

##### Saturday, July 11, 2015

Recently tried to drive an IE3 15kW induction motor via a soft start. Although current rating is 29.5 amps for continuous running, the inrush for these high efficiency motors is much higher than that of lower efficiency motors. Motor stalled on first attempt, then tripped breaker. Ok - easy to think this was an overload as it was from a 32 amp mains breaker. Upon checking windings it could be seen that U1-U2, V1-V2 and W1 to W2 were all balanced at 0.1 ohms. Yes 0.1 ohms. Not exactly the resi ...

#### 6 tips of building a trouble-free VFD system

##### Wednesday, February 18, 2015

I have used variable frequency drives (VFDs) from a number of manufacturers over the years (ABB, Gozuk, Control Techniques, Emerson, to name a few), and I have not had specific failures with any of them. What I did do:

1) Spent a lot of time up front to size the VFD properly for the application.

2) Spent time up front to research the VFD product specified to be used for the application - in ...

#### The most common causes of VFD failure

##### Thursday, February 12, 2015

Every engineer has good points about variable frequency drive (VFD) failure reasons. Some of the phenomenons occur more frequently and some are rarer.

The sizing of VFD is important. Also the application and demands of application should be studied carefully. In some case it might be better to use soft starter than use VFD. Thus VFD is suitable for wide range of applications, some parameters should be examined before installin ...

#### Asymmetrical Faults

##### Tuesday, January 13, 2015

This discussion has touched upon three topics that are each independent from the others.

1. Asymmetry due to only one or two phases being faulted
2. Asymmetry due to a DC offset of the sinusoidal fault
3. The decay of fault current with time due to differences in the reactance of generators with time (not really an asymmetry and not addressed by my comments)

The negative-sequence vectors do not rotate in the opposit ...

#### Motor Ground Fault Tripping on a VFD

##### Sunday, December 28, 2014

Case: I have a VFD installed at my plant to run a 500 hp motor. Recently we had an incident of motor tripping on Ground Fault. The motor's insulation resistance was tested & the results showed that winding was grounded. After repair, the motor was again connected to the VFD & started but the VFD tripped the motor on "Inverter Ground Current". I checked the insulation resistance of motor & cable but the values were in Mega Ohms. I even checked the VFD physically to ensure that the ...

#### How to check and test harmonics for electric drives?

##### Monday, December 1, 2014

Any non-linear load (such as a computer, a microwave oven, some refrigerators and electric stoves, or a variable frequency drive) will generate harmonics to some extent. Motors and generators themselves - because of inherent dissymmetries in the manufacture - can create some as well. The variable frequency drives that are referred to as "active front end" topologies are probably the worst, since their whole approach is to introduc ...

#### Soft Starter Fault Connection

##### Saturday, November 22, 2014

I have involved with a soft starter study recently which was about a 750 kW motor had failed to start. In the investigation, we found that there were many flaweds in the system configuration as follows:

* The power supply was slightly weak to handle the full starting current this is why a soft starter was deployed - of course - but again with the soft starter there was some voltage dip during the operation.

* The cables were laid flat rather than in trefoil. This caused ...

#### Problem of VFD controlling positive displacement pump

##### Tuesday, November 18, 2014

Problem:
Pump type is a piston dosing pump with manual struck length adjustment with motor 3 phase 220 AC volt delta connection variable speed. We control it with a GK3000-2S0007 1 hp variable frequency drive (VFD) single phase 220 VAC to three phase output. We control the dose of the pump through the VFD with analog reference signal 4-20 mA which effect the frequency (V/F) which change the motor speed rpm. The problem is at low required dosing ...

#### Frequency Converter Detecting (Troubleshooting) Steps

##### Thursday, October 9, 2014

First step: For safety, please cut off the frequency converter power before doing it.
Open the left and right side covers of the converter, as show in following figures:

Second step: Power on the frequency converter and switch on power, push the green start button, check the LED indicators will be lighting or ...