# Tap changer and generator

#### Thomas29

If a transformer on load tap changer was to be left in the manual position rather than the automatic function, what if any effects could this have on a generator which produces 10Mw ?

#### PhilCorso

Thomas29...
1) Is the Gen'r supplying a local Load-Bus?
2) Is the Gen'r supplying power to the "Grid''?
Regards, Phil Corso

#### barindra75

Can you please tell a brief about manual position and automatic function difference.

#### Thomas29

Thomas29...
1) Is the Gen'r supplying a local Load-Bus?
2) Is the Gen'r supplying power to the "Grid''?
Regards, Phil Corso
Hi Phil,
If I understand correctly then yes it is supplying the local load-Bus with power produced and the remaining power is distributed to the grid.
If our generator is offline we are pulling from the grid to supply our facility.

On the control panel for the tap changer we have an under voltage alarm present and looking at the voltage we are approx 200v below what it should be.

The control panel is this:

With the tap changer in the incorrect position and the voltage below what is normal could this have any effects on the generator ?

Thomas29...
Consider:

#### PhilCorso

The attached file uses a procedure called called the Superposition Theorem!
Regards, Phil Corso

#### Attachments

• 397.3 KB Views: 20

#### CSA

Thomas29,

The manufacturer’s instructions clearly state the equipment is to be operated by appropriately trained staff.

What is the rated voltage of the generator and the grid with which the generator is synchronized? 440 VAC? 6140 VAC? 11kV? 13.8kV? In other words, how much—in percentage of rated—is 200 VAC?

Is the tap changer at maximum position—or what position do you propose leaving it in?

How long do you propose leaving it in the one position?

Why do you feel that leaving it in one position is the best choice?

What is the voltage differential (if any) of the generator when your captive load is not being powered?

When the generator is synchronized to the grid, is there a tap changer on the main step-up transformer? If so, what position is it in? (Maximum orMinimum, or somewhere in between?)

Have you spoken with the grid operators the generator is synchronized to about the voltage differential?

What is the typical power factor the generator operates at when the voltage differential is present?

This is just a portion of the information which would be asked by a knowledgeable tap changer control manufacturer would be asking and need to know. Hard (actionable) data (printouts or electronic data) are best; anecdotal data is not very good nor reliable.

I don’t know if you can provide all the information requested above. If not, the questions are intended to be used in a logical troubleshooting process AND when gathering data for knowledgeable personnel you will most likely need to summon to site.

Since you have posted this on Control.com, we would greatly appreciate hearing the resolution as you work to resolve the issue(s).

Best of luck!

Most—but not all—synchronous generators are not designed to be operated at a large (percentage) voltage differential, which would result in “negative” VArs flowing ‘into’ the generator which can create hotspots in the generator and left unsolved can cause serious damage to the equipment.

“Negative” VArs will also mean a “negative” power factor, a value less than unity (1.0) in the Leading direction.

#### Thomas29

Thomas29,

The manufacturer’s instructions clearly state the equipment is to be operated by appropriately trained staff.

What is the rated voltage of the generator and the grid with which the generator is synchronized? 440 VAC? 6140 VAC? 11kV? 13.8kV? In other words, how much—in percentage of rated—is 200 VAC?

11kV

Is the tap changer at maximum position—or what position do you propose leaving it in?

should be in position -3 . Was left at 0 in manua

How long do you propose leaving it in the one position?

as above

Why do you feel that leaving it in one position is the best choice?

as above

What is the voltage differential (if any) of the generator when your captive load is not being powered?

Need to check

When the generator is synchronized to the grid, is there a tap changer on the main step-up transformer? If so, what position is it in? (Maximum orMinimum, or somewhere in between?)

Yes oltc on transformer but left in manual by error and at 0 rather than -3

Have you spoken with the grid operators the generator is synchronized to about the voltage differential?

not yet

What is the typical power factor the generator operates at when the voltage differential is present?
Need to check

This is just a portion of the information which would be asked by a knowledgeable tap changer control manufacturer would be asking and need to know. Hard (actionable) data (printouts or electronic data) are best; anecdotal data is not very good nor reliable.

I don’t know if you can provide all the information requested above. If not, the questions are intended to be used in a logical troubleshooting process AND when gathering data for knowledgeable personnel you will most likely need to summon to site.

Since you have posted this on Control.com, we would greatly appreciate hearing the resolution as you work to resolve the issue(s).

Best of luck!

Most—but not all—synchronous generators are not designed to be operated at a large (percentage) voltage differential, which would result in “negative” VArs flowing ‘into’ the generator which can create hotspots in the generator and left unsolved can cause serious damage to the equipment.

“Negative” VArs will also mean a “negative” power factor, a value less than unity (1.0) in the Leading direction.
*** Answers below each question thanks

#### CSA

Okay; so, the main step-up transformer tap changer is mistakenly in position 0 when it should be in position-3. Could this be the reason for the 200 VAC differential?

I’m not going to read any more of the manual than I have, and we don’t know what the “normal” positions or ranges of operation of the two tap changers is/are. We are playing a game of 20 Questions and we’re fast approaching the limit of 20 questions with very few answers and even less information.

Please have someone knowledgeable about the equipment come to your site and be prepared to provide the necessary information as outlined above.

If the problem started when the main step-up transformer was manually put into or left in the wrong position then that’s the place to start trying to resolve the problem (by putting the transformer tap changer in automatic or whatever position it should be in for the present operating conditions.

Your question has been answered. Find and consult the generator manufacturer’s Generator Capability Curve to determine if the present or proposed (by way of testing) tap changer position is within limits of the generator at your site.

Blessed day.

#### PhilCorso

CSA...
Great deduction !
Sincerely, Phil Corso

#### barindra75

Thomas29,

The manufacturer’s instructions clearly state the equipment is to be operated by appropriately trained staff.

What is the rated voltage of the generator and the grid with which the generator is synchronized? 440 VAC? 6140 VAC? 11kV? 13.8kV? In other words, how much—in percentage of rated—is 200 VAC?

Is the tap changer at maximum position—or what position do you propose leaving it in?

How long do you propose leaving it in the one position?

Why do you feel that leaving it in one position is the best choice?

What is the voltage differential (if any) of the generator when your captive load is not being powered?

When the generator is synchronized to the grid, is there a tap changer on the main step-up transformer? If so, what position is it in? (Maximum orMinimum, or somewhere in between?)

Have you spoken with the grid operators the generator is synchronized to about the voltage differential?

What is the typical power factor the generator operates at when the voltage differential is present?

This is just a portion of the information which would be asked by a knowledgeable tap changer control manufacturer would be asking and need to know. Hard (actionable) data (printouts or electronic data) are best; anecdotal data is not very good nor reliable.

I don’t know if you can provide all the information requested above. If not, the questions are intended to be used in a logical troubleshooting process AND when gathering data for knowledgeable personnel you will most likely need to summon to site.

Since you have posted this on Control.com, we would greatly appreciate hearing the resolution as you work to resolve the issue(s).

Best of luck!

Most—but not all—synchronous generators are not designed to be operated at a large (percentage) voltage differential, which would result in “negative” VArs flowing ‘into’ the generator which can create hotspots in the generator and left unsolved can cause serious damage to the equipment.

“Negative” VArs will also mean a “negative” power factor, a value less than unity (1.0) in the Leading direction.
Kudos... And exact