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DG Speed Variation

05/24/2021 7:36 AM

We have a Wartsila 2MW DG with woodward governor 721.The DG speed varies with no load from +/- 10 Rpm.Its rated speed being 750 rpm.

The OEM says that its tuning issue and suggested to alter its gain and reset settings.

We have tried changing the gain from 1.2 to 1.8 and reset from 0.2 to 0.3 but to no avail.

Kindly suggest the way forward.

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Pathfinder Tags: woodward governor 721 tuning
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#1

Re: DG Speed Variation

05/24/2021 12:08 PM

Does it do the same under load?

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#2

Re: DG Speed Variation

05/24/2021 1:08 PM

You may wish to investigate training opportunities here:

https://www.wartsila.com/wlsa

Here is a description of one of their courses.

Power Plant (Diesel) Electrification
1. Target group
This training course is aimed for power plant personnel at the operational and management levels.
2. Prerequisites
The trainees should have a basic knowledge and operational experience of large medium speed engines. Theoretical education on internal combustion engines is preferred.
3. Objective
The participants will understand the working principles and operational function of each electrical system in the power plant thus enabling them to operate the plant in a safe and effective way.
4. Duration
Recommended duration five (5) working days.
5. Content
· General Electrical Plant Design and Operation Modes
· Engine control, Instrumentation and Automation systems
· Alternator and Automatic Voltage Control
· Plant Control and Monitoring System
· Power Distribution System

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#3

Re: DG Speed Variation

05/24/2021 1:24 PM
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#4

Re: DG Speed Variation

05/24/2021 7:44 PM

You set the gain higher, but oscillation may indicate that the gain is too high.

"Carefully adjust Gain. You are looking for the best compromise between quick response and good stability. Make very small adjustments, then load and unload engine, or pull linkage back slightly and release. Usually, a good set-up is one that makes 1 to 3 small bounces and then steadies down after a large load change. Too much Gain shows up as a rapid (once per second) instability, most commonly at light loads. Too little Gain shows up in large over-shoots on start-up or large load changes, and generally sluggish operation."

http://www.pgcontrols.com/wp-content/uploads/2015/06/E-381-Manual.pdf

Try reducing the gain.

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#5

Re: DG Speed Variation

05/24/2021 8:00 PM

Here is a document that describes the interaction of reset and gain.

https://www.woodward.com/-/media/publication-assets/technical-manual/2019/4/18/19/58/82020.pdf

See section on "Adjust for Stable Operation".

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Participant

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#6
In reply to #1

Re: DG Speed Variation

05/24/2021 9:11 PM

It is steady under load.No variations.

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#7
In reply to #3

Re: DG Speed Variation

05/25/2021 12:54 AM

Thanks but This link is not working.

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#8

Re: DG Speed Variation

05/25/2021 1:42 AM

Please describe condition on load, normally on-load variation reduces. Also check quality of fuel/fuel lines, filters etc for clearance. Adjust gain slowly, normally works better on lower value of gain.

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#9

Re: DG Speed Variation

05/25/2021 3:24 AM

Has it always behaved this way? If not, what changed on the mechanical side?

I have found that fuel injection control arms and pump racks can affect the governor response. In idle mode, close to minimum fuel, if a few pumps have issues, you will have hunting.

When under load do you mean grid connected?

What actuator do you have?

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#10

Re: DG Speed Variation

05/25/2021 6:39 AM
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#11
In reply to #10

Re: DG Speed Variation

05/25/2021 7:06 AM

If it's stable with no load, then it will be stable when loaded.

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#12
In reply to #5

Re: DG Speed Variation

05/26/2021 3:07 AM

Pages 15-19 describe, loosely, the Ziegler-Nicholls method of tuning control loops.

GA

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#13
In reply to #8

Re: DG Speed Variation

05/26/2021 10:12 AM

It's got nothing to do with <...fuel/fuel lines, filters etc...>, because the equipment works normally on load and only misbehaves when the load is low. Were there to be a fuel supply problem then it would trip off on low fuel supply when under load.

Sorry.

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#14

Re: DG Speed Variation

05/31/2021 4:06 PM

If this is a sustained oscillation:

Set Reset to zero.

Time the oscillation,in times per minute.

Take the reciprocal of this time period and use it for reset value.

Set derivative at 1/8 of this value.

These are good starting points.

Fine tune from this point and use very small adjustments.

Ideal tuning is when,after an upset(An applied load),it returns to set point within 4 cycles without overshoot or lag with each cycle 1/4 of the preceding cycle amplitude.

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#15

Re: DG Speed Variation

06/01/2021 12:05 AM

The speed variations in no load condition are reduced considerably after we increased the gain to 3.1 from 1.2 default value.

The reset is brought back to default value of 0.2 secs from 0.3 secs.

The actuator compensation is left at its default value of 2.0 secs.

Now the speed variations are within +/- 2 rpm.

We are now able to synchronise another dg in parallel which we were struggling when the speed was varying.

Thanks everyone for your valuable time and efforts.

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