basic generator operations

Operations Introduction to GE’s Generators

Basic Operations

• The following information is intended to be used an introductory guide only and is not intended for actual plant use.

Operations Introduction to GE’s Generators

Starting the Generator for the first time.

• The following inspections and preliminary checks should be made before the generator is started for the first time.

• Check all connections IAW the provided Connections Outline.


Connections

• See that the voltage on the generator nameplate corresponds with line voltage.


Voltage

• Check RTD’s for proper operation IAW provided technical documentation.


RTD’s

• Inspect the generator for gas leaks.


Mechanical Tightness

• The collector Rings should be carefully inspected for scratches or rough spots.

• Brushes should be seated to the collector rings.

• The position of the brushes and associated rigging should be set IAW applicable technical documentation.


Collector Rings and Brush Rigging

• The insulation resistance of the stator and the rotor should be taken IAW applicable technical documentation.


Insulation Resistance

• The shaft sealing system must be in operation IAW instructors for the Hydrogen Cooling System.


Shaft Sealing System

• The fan and rotor clearances should have been checked during construction. Records should be reviewed to ensure that this has been done.


Clearances

• As specified in bringing the generator up to speed, checks should be made to insure that there is no rubbing between rotating and stationary components of the generator, and that operation of both the turbine and and the generator rotors are free of excess vibration.


Rubbing and Vibration

• The bearing and seal housing insulation should be checked IAW applicable documentation.


Bearing and Seal Housing Insulation

• The exciter should be checked thoroughly IAW applicable excitation technical information.


Exciter

• Should be inspected IAW applicable technical documentation.


Hydrogen System

• The gas coolers should be checked to ensure that all coolers are full of water and have been vented.

• The water supply to the coolers should be properly throttled to prevent over heating or causing condensation to form.


Gas Coolers

Starting the Generator

• When starting the generator, it is recommended that a startup check list be used to ascertain that no items have been over looked. The following items should be included on a checklist.


Conventional Starting Motor

• Armature Circuit Breaker OPEN• Main Field and Spare Breakers OPEN• Voltage Regular selected to Manual • Manual Voltage adjust in the LOW position



• When the unit is turning slowing, check for Rubbing.

• As the generator is brought up to speed, check for mechanical balance by monitoring shaft vibration readings.

• Check the position of the collector ring brushes. Ensure that they are riding properly and not sparking.



• Regulate the cold liquid flow valves to obtain the rated flow condition.

• Cold gas temperature will be a function of cold liquid temperature.


LCI Starting System

• LCI controls are properly set per Turbine Operating Instructions.

• Generator grounding transformer breaker is OPEN• LCI Safeties are Reset and Operational.• Generator Safeties are Reset and Operational


LCI Starting System

• When the unit is rolling slowly, check for Rubbing.

• Check the position of the collector ring brushes. Ensure that they are riding properly and not sparking.

• Verify that Hydrogen pressure and purity are at rated conditions.


LCI Starting System

WARNING• Startup of a Hydrogen cooled generator in air is

significantly harder on the generator due to the reduced heat transfer properties of air. For this reason any low speed hold points typical of those associated with Water Wash, Purge, and HRSG warm-ups must be eliminated. The transition from turning gear speed to rated speed must be as quick as possible.


LCI Starting System

• Regulate the cold liquid flow valves to obtain the rated flow.

• As the generator is brought up to speed, check for mechanical balance by monitoring shaft vibration readings.

• RTD’s should be checked frequently during startup to determine that winding temperatures are not excessive.


LCI Starting System

• At 90% speed, verify that the LCI is de-energized and that the circuit breaker between it and the generator is OPEN.

• Verify that the LCI breaker is OPEN.• Verify that the breaker between the generator

neutral and the grounding transformer is OPEN.

Before Synchronizing

Build Up of Generator Voltage

• After the unit is up to 95% rated speed or greater, Close the Main Field Breaker.

• Set the regulator control switch to “Start Up” for approximately 5 seconds ,“Flash the Field” and release.

• Check that the generator’s voltage has built up.


Set No-Load Excitation

• Adjust machine terminal voltage with the Manual-Volts adjust.

• Set terminal to voltage to match bus voltage.


Transfer to Automatic Voltage Regulation

• Set the regulator control switch to “TEST”.• Zero the transfer voltmeter by means of the

automatic voltage adjuster.• Set the regulator control switch to “Auto”.• Recheck the generator voltage with bus voltage.

Synchronizing the Generator

Requirements for Synchronizing

Prior to synchronizing the following requirements must be met.

Frequencies Matched

Voltage Matched

Same Phase Sequence


Match Generator Frequency to Bus Frequency

• Adjust turbine speed to a slow rotation of the synchroscope, or

• Use automatic synchronization.


Match Generator Voltage to Bus Voltage

• Set the automatic voltage adjuster to match generator voltage to bus voltage, or



Match Generator Phase Angle to Bus Phase Angle

• When the synchroscope reads zero, close the generator breaker, or


Improper Synchronizing

What would happen if the requirements to synchronize

(parallel) were not met and the generator output breaker was

shut?


Frequency

If frequency was not matched several things would occur:

1. It would be difficult to match the phase angle between the incoming and running machines.

Remember: For two “machines” to have the same phase sequence, their frequencies must be the same.


Frequency

2. If the incoming machine’s frequency (the generator) was less that the running frequency (the power grid), the generator would be a real load on the grid.


Voltage

If voltage was not properly matched several things will occur:

1. It would be difficult to match the phase angle between the incoming and running machines.

more importantly


Voltage

2. Excessive damage will result to the generator, the output breaker, and possibly the grid due to extremely high circulating currents and uncontrolled power transients.


Voltage

“What would happen if the generator output breaker was shut with generator voltage not matched to grid voltage?”


Voltage

Initial Conditions

Generator (incoming) is rated for 13.8 kV

Grid (running) is 15.0 kV on the LV side of the HV Step-Up transformer.


Voltage

A rough estimation of the voltage difference across the breaker can be

made as follows:

Convert 13.8 KV and 15.0 KV to Peak Voltages.

PK = RMS/.707


Voltage

Generator

PK =13,800 volts/.707

PK = 19,519 volts


Voltage

Grid

PK =15,000 volts/.707

PK = 21,216 volts


Voltage

The voltage difference between the Generator and the Grid is:

Running - Incoming = Volts

21,216 volts - 19,519 volts = 1697 volts


Voltage

Using a design resistance of .01 , the amount of instantaneous current and

power can be calculated.

Ohm’s Law

I = E/R

I = 1697 volts/ .01

169,700 amperes


Voltage

Power (watts)= I2 x R

Power (watts) = (169,700 amps)2 x .01

Power (KW) = 287,980.9 KW!


Phase Angle

Improper phase angle is caused by improperly matched voltages and

frequency.

However, with all of the conditions met, it is still possible to parallel out of phase simply by shutting the breaker at the wrong time during the paralleling sequence.


Phase Angle

“What would happen if the generator output breaker were shut when the

“synchroscope” was at the 11 o’clock position.”


Phase Angle

Initial Conditions

The Generator (incoming) and Grid (running) voltages are matched and are

at 13.8 KV.

PK =13,800 volts/.707

PK = 19,519 volts


Phase Angle

Make the assumption that a synchroscope is similar to a clock.

At the 11 o’clock position, the running and incoming voltage phases are 30o

apart.


Phase Angle

Since the generator is being paralleled to the grid, we will assume that the grid

voltage is stable.

Therefore, we must solve what the generator voltage is when it is 30o out of

phase with the grid.


Phase Angle

It becomes a simple math problem.

Generator Voltage = PK (cos )

Generator Voltage = 19,519 (cos 30o)

Generator Voltage = 16,903.9 Volts


Phase Angle

The difference in voltage between the Grid and the Generator is found as follows:

Grid (running) - Generator (incoming) = Volts

19,519 volts - 16,903.9 volts = 2615 volts


Phase Angle

Instantaneous current and power can now be calculated using a design resistance

of .01 ,

Ohm’s Law

I = E/R

I = 2615 volts / .01

261,500 amperes


Phase Angle

Power (watts)= I2 x R

Power (watts) = (261,500 amperes)2 x .01

Power (KW) = 683,822.5 KW!

Initial Loading

• Pick up approximately 3-5% rated load immediately after the generator breaker has shut.

• Adjust the automatic voltage regulator to achieve the desired power factor.

• RTD’s should be checked to ensure that winding temperatures are not excessive.

• Cold Gas temperature should be maintained between 30 to 40 oC (86 to 104 oF) with a maximum of 46 oC at 30 psig (207 kPa) hydrogen pressure.

Droop operation is used for generators connected to the grid.

Operating on the Power Grid


This allows generators to share load changes that occur in proportion to their maximum rating.


This occurs regardless of what the actual load is on any particular machine at any given time as long as the

unit is “on-line” and does not exceed rated load.


If there is a load change with multiple generators in the system, this formula is used to determine what the new load would be for a single generator based on a particular system load change.

For Example. In this power system there are three 60 Hz generators with a 4% droop. If the ACME coffee factory creates a sudden 15 MW demand, what will happen to each generator?

Multiple Turbine Operation

What would the new load demand be for Generator #2?


258.8 MW


Single Turbine Operation

To see how droop operation affects a single turbine generator connected to a distribution system, the following problem provides an example.

Example: Calculate the new speed when a 25 MW load is started on a 100 MW generator operating at 60 Hz and 3600 RMP with a 4% droop?


This problem is simple if you remember that speed droop in linear!


From No-Load (NL) to Full Load (FL), the generator will experience a change of 100 MW.

This change should only change running frequency by 4%.

Therefore:


NL-FL = 100 MW

60 Hz x .04 (% droop) = 2.4 Hz

25 MW load demand

100 MW = 25 MW

2.4 Hz X

100 MW (X) = 25 MW (2.4 Hz)

100 MW (X) = 60 MW(Hz)

X = 60 MW (Hz)

100 MW

X = .6 Hz

60 Hz - .6Hz = 59 .4 Hz


The formula for Frequency is:

F = NP / 120

F (120) =NP

F(120) = N

P

(60 Hz - .6 Hz) x (120) = 3564 RPM

2

Where: F = frequency in Hz

N = Speed in RPM

P = number of machine poles (2)


At anytime during this speed reduction, the operator can manually restore frequency to

60 Hz by raising the called-for speed to reach 3600 RPM.

The called - speed set point of the turbine can be adjusted automatically by the use of

automatic control system.


Power Factor (pf) Adjustment• If the generator is operating as a single unit, power factor

is determined by the load.

• When the generator is operating on a system with other generators, power factor is determined by the generator field current.

• Power factor maybe adjusted by changing the field current; for over excited operation (Lagging pf), increasing the field current will lower the power factor.

• Lowering the field current will raise the power factor (Leading pf).

Effects of Leading and Lagging Power Factor

• Because of system conditions, generator’s are usually not operated at rated pf. It is important for operators to understand the limitation of the generator during this type if operation.

Effects of Leading and Lagging Power Factor

• Capabilities and limitation of a generator are best illustrated using the Reactive Capability Curve.

Reactive Capability Curve

• This curve shows the relationship of KW, KVAR, and KVA.

• It also shows what generator limitations are at different operating conditions.


• The curve has three outside cures that represent inlet cold gas or air temperatures.

• The colder the temperature, the higher the loading capability.


• There are rated pf limit lines that intersect the cold gas curve.

• Operating points are established based on current pf, Real Power (MW), and temperature.


• The gas curve is broken down into limiting regions.

• Operation outside of these areas can have adverse effects on generator performance and possibly, lead to damage.

Reactive Capability Curve• The portion of the

curve extending between Rated pf -Lagging and the .95 pf-Leading line is an arc whose radius of 1.0 per unit KVA corresponding to the rating at various hydrogen pressures.

Armature Winding

Limits


• In this region, KVA is limited by armature winding temperature limits.

Armature Winding

Limits


• In the region between the Rated pf-Lagging (over excited) and the zero-pf line, KVA is limited by the temperature rise of the field winding.

Field Winding

Heating Limits


• In the region of Leading-pf, rated KVA can usually be carried to .95-Leading.

• After this point, KVA is limited to minimize end iron heating of the armature core.

End Iron Heating

Shutting Down the Generator


• Reduce Load on the generator to zero by adjustment of the synchronizing device on the turbine.

• When load has been reduce to zero, open the generator breaker.

• Adjust the transfer voltmeter voltage to zero by use of the manual voltage regulator.

• Switch the regulator to Manual.• Reduce machine terminal voltage to the minimum

value.


• Open the Main Field Breaker.• Secure water to the cooler when the turbine is shut

down.

Generator Casualties

Loss of Field

• Operation of the generator connected to a power system without field current will cause excessive field heating.

• The degree of heating depends upon initial load, the manner in which the field was lost, and the manner in which the generator is connected to the system.

Concerns

Loss of Field

• When excitation is lost, the generator tends to overspeed causing to act as an induction motor.

• This overspeed results in a reduction of load ,an increase in armature current, low voltage at the generator terminals, and very high rotor currents.

• Rotor currents will flow through the field winding (provided that the field winding has been short-circuited or is connected through a field discharge resistor) and through the rotor body, completing a circuit through the rotor coil wedges.

Concerns

Loss of Field

• Circulating rotor current will cause extremely high and possibly dangerous temperatures in a very short period of time.

• The time required for the heating to become dangerous depend upon the conditions of the loss of excitation.

• Generally, this time is short beginning in a matter of second rather than minutes for a machine with an open field winding.

Concerns

Loss of Field

• Opening of the field circuit with the machine carry a load, will subject the windings to high and possibly dangerous voltage levels from the inductive effects of the windings.

Concerns

Loss of Field

• If excitation is lost by accidental tripping of the field breaker, the breaker should immediately be re-closed without shutting down the machine.

Actions - Accidental Tripping

Loss of Field

• If the machine is discovered to be operating without field for an unknown period of time, it should be immediately be tripped “off-line” and shut down for inspection to determine the degree of rotor damage.

Actions - Unknown Tripping

Loss of Field

• Relays are know available that determine when a machine has started slipping due to loss of excitation.

• Since the heating effect occurs in a relatively short period of time after the loss of the field, the relays are employed to trip the machine “off-line”.

• Damage will(should) be prevented from overheating and the machine may be placed back in service as soon as the defect in the excitation system has been remedied.

Actions - Unknown Tripping

Grounded Field Winding

• It is general practice to operate the generator excitation system ungrounded.

• If an accidental single ground occurs on the generator field operating on an ungrounded system, no change in excitation should occur, but the machine should be removed from service because of the risk of system interruption and damage to the generator field.

Concerns

Grounded Field Winding

• After a ground is indicated, the generator should be removed from service and the cause of the ground located and repaired.

• In no case should the generator be allowed to remain on the system for any appreciable time after a ground has occurred.

Actions

Generator Load Capability

• The generator should not be allowed to operate at any loads above the nameplate rating even though operating temperatures are well below rated temperatures.

• Intermittent operations of loading beyond the nameplate values encroaches on the design margins built into the machine.

basic generator operations

Education

generator lci

generator safeties

generator rotors

generator nameplate

hydrogen cooled generator

hydrogen system

iaw applicable documentation

system lci controls