Effect of Generator driving nonlinear load- varies speed drives (VFD)

[omime]

Dear all,

Our plant have two Gas-turbine generators, rated 2*2.8Mw supplying electricity to all consumer. The starting system of this turbine consists of Diesel generator(220kW,3ph,380V,50hz,417A)feeds to VFD(rated 100-150Hp/210A)driving the starting motor(50HP/90A). Our problem is there is voltage fluctuation 350-530 V generated from generator ( speed variation 1482-1517 rpm) whist starting turbine sequence and having additional loading (motor isolated after staring seq. completed). I would like to have your assistance to provide the expertise/professional recommendation and solution on that matter as follows :

1)Is this problem effected of diesel generator driving non-linear load-VFD, if so, that means that diesel generator is derated, in general, how much does power of gen.(%)give off to non-linear load?
2)How the outcome to solve this problem?

I'll be much obliged and welcome for any comments.
Thanks nad best regards, omime

 

[jbartos]

Please, provide the following info:
1. Is this a new project or is it an existing project?
2. Was the motor load added or is there per original project designs?
3. Was VFD added or is there per the original project designs?
4. What kind of votage regulator the Diesel Generator has?
5. Is there a flywheel at the Diesel Generator set?
6. Does the project have any analysis or calculation documents available, supporting this design?
The solution to the irregularity may require transient, load, and harmonic analyses via a suitable electrical software.

 

[omime]

Dear sir,
Thank you for your answer, dated Nov2, 2000. We would like to provide further information further to
Commonly, a diesel generator is used to provided power for staring the turbine in a "Black Start" situation.

Starting cycle :
When the start/crank cycle is initiated, Variable Frequency Drives(VFD) drawn the power from diesel generator, provides a low frequency and voltage(PWM) to starting motor to begin rotation. The frequency and voltage to motor ramp up to accelerate to 1st speed setpoint( turbine purging speed), When purging cycle is completed. VFD increases frq. and voltage to a new acceleration 2nd speed setpoint to motor, thereby increasing turbine speed to the ignition point. This speed maintains until ignition is successful. Engine continuous to dropout speed, VFD is de-energised, cutting power to the motor, and the motor clutch is disengaged.

Crank soak wash cycle :
Chemical water spays to turbine to wash its blade at low speed ( 1st speed setpoint) in accordance with Turbine preventive maintenance schedule.

In response to your queries :
1)"Black Starting" system was implemented since 1998
2)Additional load to motor is spaying chemical water injected to turbine during Crank soak wash cycle.
3)VFD must drive the starting motor for turbine engine cranking begins as per original design.
4)We use analogue voltage regulator for self excited generator. ( type SR3F, "caterpillar&quot
5)Yes, fly wheel places at coupling side(between engine to generator)
6)Unfortunately, we don't have now all in hand, however, we are deal with Original contractor in requesting those documents.

If there are any queries, please feel free to contact me.

Best regards, omime

 

[jbartos]

Suggestions:
1. The voltage regulator (SR3F) needs to be checked for proper functioning. If damaged, do not replace by new one unless the harmonic content from 2. is analyzed/mitigated first since it could be damaged again.
2. The harmonic content on the VFD input side needs to be analyzed and found acceptable or mitigated to be acceptable (e.g. by filtering).
3. Waiting for the documentation and the Contractor support is recommended since the similar problem may be in existence elsewhere and an adequate solution is available.

 

[omime]

Dear Mr.jbartos,

Referring to your suggestion item 2,before go ahead to replace a new voltage regulator I have some more questions :
1) How/procedure to record the waveforms of current and voltage and measure the harmonic content in the line ?
2) What is the instrumentation of measurement the harmonics propagated form VFD up to the Diesel Generator ?

Best regards, omime

 

[jbartos]

1. A harmonic analyzer is the device that is connected to power line to monitor voltage, similar as voltmeters, and currents, similar to clamp-on transformers. When all connected, one analyzes voltage, current and power simultaneously.
2. The harmonic analyzer is an essential instrument to display harmonics on its display. There are several manufacturers who offer this product and instruction/users manual to set up the measuring scheme. The harmonic analyzer may come in simple version with essential features to measure harmonics and other parameters. I also may have many features, which you may or may not need, such as data logging for prolong monitoring and recording. May I suggest that you contact some of the following businesses to obtain more specific information for your measurements/analyses and needs:
1.
Valhalla Scientific at 858-457-5576 Tel, 858-457-0127 Fax or

http://www.valhallascientific.com/homepage.html

It offers Valhalla 2100 Series, Valhalla 2400 Wideband Spectral Power Analyzer and Valhalla 3030A Energy Analyzer Dataloger. Up to four clamp-on transformers may be needed (3 phases and neutral).
2.
RS Electronics, 1-800-555-5312 Tel, rselectronics@rselectronics.com

http://www.rselectronics.com

which offer Fluke 40 series ($1995) and Fluke 39 Series ($995)
3.
Visit

http://www.instrumentation2000.com

for a catalog covering harmonic test instruments, 1-888-476-3728 Tel
4.
Davis Instruments, at 1-800-368-2516 toll free tel and 1-800-433-9971 toll free fax
cbost@atdavisontheweb.com

http://www.davisontheweb.com

for Rustrack Ranger Power Logger Model RR2-1258W-4 ($5,195.00, which appears to be more expensive, however, it complies with IEEE 519 and IEC 555 Standards). Once the harmonic contents are known (total harmonic distortion (current and voltage), single current and voltage harmonic distortions), additional steps may be taken. Also, service firms may be contacted to solve your problems if this appears to be difficult for you.