ML17339A565

Ro:On 740301,output Voltage Began to Oscillate.Operator Attempted to Stabilize Voltage by Controlling Generator Voltage Manually.Caused by Lowering Machine Voltage During Min Load Periods

ML17339A565
Person / Time
Site:	Turkey Point
Issue date:	03/25/1974
From:	Schmidt A FLORIDA POWER & LIGHT CO.
To:
Shared Package
ML17207A819	List: ML17207A818 ML17339A563 ML17339A565 ML17339A567 ML17339A569 ML17339A571 ML17339A572 ML17339A574 ML17339A575 ML17339A576 ML17339A577
References
NUDOCS 8002150478
Download: ML17339A565 (5)

Text

g<Cgg Reference 4 PLORIOA POVVKR 5 LIGHI'OMPANY March 25, 1974 Mr. Norman C. Moseley Director Region II Directorate of Regulatory Operation U. S. Atomic Energy Commission 230 Peachtree Street, iN. N., Suite 818

~

Atlanta. Georgia 30303.

Dear Mr. Moseley:

TURKEY POINT PLAiNT DOCKET NOS. 50-250 5 50-253.

UNIT TRIPS - MARCH 1, 1974 The following information is submitted in response to your tele-phone request of March 4, 1974, and is based on review. of plant

~

records (logs, data sheets and charts), statements by operating personnel on shift at' the time of the trips, and data provided by our system operations department.

DESCRIPTION OF OCCURRENCE On Friday, March 1, 1974, the Turkey Point k4 Unit was increasing load after a reduction test (504 load reduction test portion of the start up. test program) which had occurred at 1:15 Ai>I. The unit was generating 640 MN, the voltage .regulator control was switched from the automatic to the manual mode. The output vol-tage of this unit began to oscillate and the operator attempted to stabilize the voltage by controling generator voltage manually.

At the same time, there were oscillations of the power output of the Turkey Point 43 Unit which was generating 750 Mtf. Turkey Point I4 Unit tripped due to loss of field and the Turkey Point t3 Unit was tripped by the operator.

The minimum system frequency recorded during the transient was 58.95 Hertz. Underfrequency load. shedding relays reduced the

" interconnected system electrical load by 387 Mlle by automatic opening feeder breakers. This caused short term power inter-ruptions scattered over peninsular Florida.

80OSZSO+>

HEI.PING BUILO FLOPIIOA

'L I

ir. Norman C'. Moseley Page 2 ((

March 25, 1974 I

The underfrequency relay trips shed the system load as follows:

0 Florida Power 5 Light 197 MN Jacksonville Electric Authority 75 MN Florida Power Corporation . 60 MN Tampa Electric Company 35 MN Orlando Utilities Commission 20 MN TOTAL 387 MN There wege no critical loads lost as a result of the disturbance.

Most of the shed load on the Florida Power 5 Light Company system was restored within thirty minutes and the maximum outage time was two hours sixteen minutes.

Both units were placed in safe hot shutdown condition and various required maintenance was performed including inspection and check F3 of Unit 84 generator, exciter and voltage regulator and the Unit voltage regulator.

Turkey Point Unit 83 was returned to service dt 2:20 PM, March .'.,

1974, and Unit Il4 was returned to service at 3:14 PM, March 1, 1974.

ANALYSIS OF OCCURRANCE In order to conserve fuel oil, both Turkey Point nuclear units are operated at maxim m power a ound the clock. During the minimum load periods, the units have operated with a leading power'factor; i.e., taking reactive power down from the system. In order to attempt during the minimum load periods, to hold the system voltage the machine voltage is lowered, causing the machine to operate in the lead and approach its stability limit.

Preoperational Test Procedure T-0201.24, Large Load Reduction, had been performed on Turkey Point Unit 44 at 1:15 AM. This test had.

been successfully completed and unit load was being increased in an orderly fashion after the test. Voltage. oscillations affecting both Unit Nos. 3 4 4 had occurred on the evening shift February 28, 1974, and Unit F3 voltage regulator had been'in manual control since that time. A decision was made to attempt to place both Units 3 g 4 voltage regulators in automatic. In view of the vol-tage oscillations experienced earlier with both voltage regulators in automatic, it was decided to place Unit 84 voltage regulator in test, then place Unit t3 voltage regulator44 in automatic and monitor for oscillation. If none occurred, Unit voltage regulator would then be returned to automatic. This operation was in progress and Turkey Point Unit k4 tripped from 640 !I!fe a1most immediately after its voltage regulator was transferred from automatic to manual con-trol and a voltage transient was experienced. The cause of the trip was loss of field which actuated the generator lockout relay.

Mr. Norman v. r'losel.e)'age 3

25, 1974

'('arch Turkey Point Unit3 tripped approximately one minute later from about 750 Mlle during the transient following the trip of Unit F4.

Initial findings that overpower hT Reactor trip was the initiating event have been discounted by subsequent-detailed investigation and it now appears that the cause of the Unit N3 trip was premature ac-tuation of the turbine manual trip pushbutton.

The oscillation observed at Turkey.:..Point, before the loss of the two units are indicative of system instability. Since these units were operating at light excitation, full load and with the voltage re-gulators in the manual mode, it is concluded that the I3 generator reached the stability limit and its variations along with the manual readjustment of the k4 voltag'e regulator caused the 84 generator to trip from loss of field,.

PREVENTIVE ACTION The following measures are being taken by FPL to avoid repeti-tion of this occurrence:

1. The problem of machine stability has been recognized and procedures'o avoid instabilities'will be estab-lished..

2. Stability limit curves are being prepared. for each unit on the system and will be issued to System Oper-ations dispatchers and power plant operating personnel with instructions not to exceed the prescribed limit.

(Voltage limits for each unit will be established with a 15: margin above the stability limit)..

3. 50,000 KVAR of distribution capacitors have been removed from the system to reduce the lead'ing reactive power on

'ill units during the minimum load periods. These capacitors be reconnected as soon as the minimum load level of the system will permit.

4. The voltage regulator settings of Turkey Point Units 3 4 4 have been reviewed and. revised, and both Units 3 4 4 voltage regulators are now operated in the au-tomatic mode.

If you have any further questions about this occurrence, please do not hesita.te to call me.

Very truly yours, c mx dt.

Director of 'Power Resources GEL/kmw C

cc: Mr. J. F. O'eary Mr. Jack R. Newman