AVR

Reliability Issues of Generator Control & Protection System at PH#5

Smarak SwainManager, IEM

Under the guidance of:

Mr. D.B.GhoshSenior Manager, IEM

Problem Statement

Reliability issues pertaining to uninterrupted supply of power

Necessary changes in generator control system for effective control

Fool-proof protection of generator through modern numeric system wherever needed

Lower maintenance cost by moving towards automation

Constraints

Though PH#5 is new, most equipments are old. System brought from PH#3

Generator excited by separate DC generator PH#5 runs at low manpower. Low manpower

is the need of the hour to stay competitive in the industry

Exciter Upgradation

Separate DC Excitation Brushless Excitation Static Excitation

Separate DC Excitation System

Static Excitation for PH#5

Carbon dust from commutator brush wear causes stator overheating

There are commutator problems such as sparking & rotor earth fault caused by carbon dust

Oil leakage is a major problem in DC exciter of PH5 Static excitation improves efficiency Faster time response Safety concerns

Digital Voltage Regulators (D-AVR)

Far more reliable than analog system Multiple operating Modes: PF, VAR modes D-AVRs provide fast transient performance for

improved voltage response to system disturbances Programmable generator voltage soft start to build

voltage to rated output eliminating need to start in manual

Human Machine Interface Analog AVR in PH5 often faces the problem of

hunting

BHEL AVRs

PROS Most electrical and

electronic instruments in PH5 are of BHEL make. Easier retrofitting possible

We have been dealing with BHEL for a long time

BHEL’s loyal and prompt service makes it a favourite

CONS BHEL’s products are

usually not its own R&D products. Products are not the latest in market

BHEL’s digital-AVR is costly

Few monitoring and add-on facilities available in excitation systems of other vendors are not available

ABB AVRs (PROS)

All logical and sequential control functions for different modes of operation are built-in, and so there is no necessity of any engineered applications like stand-alone PLC programs

Control interface to the control room available through remote HMI facility

Built in Data Logger allows System Debugging over wide time areas

Built in Fault Logger stores up 99 Faults Static excitation system (~70 lacs) cheaper than

that of BHEL excitation system (~80 lacs)

GE Energy D-AVRs (PROS)

Incorporates most advantages of ABB AVRs IGBT based digital controller provides faster

variation in firing angle compared to thyristor based controls

Digital AVR supplied by GE Energy (~ 10 Lacs) is far cheaper than those by ABB (25 Lacs) and BHEL (40 Lacs)

Auto-synchronizer is an optional integrated feature in case of GE Energy system

ABB & GE Products (CONS)

There are apprehensions about performance of ABB & GE Energy systems. GE Energy salesperson has however provided a list of plants using their products world over. Contacts of their customers in India have also been provided

Doubts regarding prompt service and expert commissioning engineers persist

Parts are shipped from abroad. Availability of spares may be a problem

Since GE Energy’s EX2100 doesn’t have a big market in India, they may not have expert technical staff in India

Budgetary Allocations

BHEL (Approximate Figures) One D-AVR: Rs.40,00,000 Three D-AVR: Rs.120,00,000

GE ENERGY (Approximate figures) One Digital AVR: Rs.10,00,000 Three Digital AVR: Rs.30,00,000 Two Spare AVR: Rs.20,00,000 Total: Rs.50,00,000

Protection Relays at PH#5

All relays in generation protection panel are old solid-state relays

Slow response Malfunctioning of some relays No provision for self-diagnostics and testing Large Maintenance Related Shutdowns Problems in fault monitoring Over-heating of relays

Cautions…

Critical failure in a numerical relay can degrade protection more significantly than a failure in older systems. Adequate backup protection should be provided accordingly

Numerical relays are microprocessor based relays. Most operators being in the middle and upper age group need to be trained on its operation and monitoring.

Making a retrofit numerical relay connection shall require overhead costs other than just the cost of relay installation

Budget

APPROXIMATE COST OF INSTALLING NUMERIC RELAYS WILL BE:

Cost of Numerical relay: Rs.3,50,000

Cost of back-up relay: Rs.3,50,000

Overhead: Rs.2,00,000

(Accessories and installation cost)

Total Cost Rs.9,00,000

Budgetary Rationale

Power Cost/KWH (as per LDC): Rs.1.8

Power Cost/MWH: Rs.1800

Power output of generator in 1 hour:Rs.43,200 (24MW average production)

Uptime for Rs.9 lacs revenue: 900000/43200 = 20.833 Hours

If we can prevent a downtime of 21 hours, due to maintenance shutdown or breakdown, we can recover the financial investment.

Thank You

Numeric Relays

NUMERIC PROTECTION

OLDER RELAYS

100% Stator Protection

95%

Complete Over-exitation Protection

Two Set Point Over-exitation Protection If Any

Unbalanced Armature Current Protection

Negative Sequence Protection provided

Frequency tracking Algorithm

Poor Frequency Response