8/9/2019 Grounding Hybrid High Resistance Grounding Solutions SA02703007E

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 P o w e r S y s t e m s E n g i n e e r i n g      

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 G r o u n d i n g Catastrophic Losses Resulting

from Generator Failures

When it’s absolutely critical to keep your equipment running,a generator failure can be catastrophic for processes andprofits. Losses at industrial facilities can exceed a milliondollars a day!

In most cases, there is no warning of an impending generatorfailure, but as equipment and processes become increasingly

more sophisticated, the impact of such an event is tremen-dous. Until now, grounding solutions haven’t kept pace with

 the growing magnitude of the problem.

Research Leads toNew Discoveries

An IEEE working group, comprised of a fellow engineer fromEaton and other experts in the field, was formed to address

 this complex issue. Their charter: to research catastrophicindustrial generator failures due to internal ground faults anddevelop a solution.

This accomplished team of professionals studied the problem

for seven years and first determined that internal generatordamage is caused by two components: the external groundfault sources and the internal generator’s own low-resistancegrounding resistor. A key finding was that most of the dam-age was caused by the low-resistance ground source inside

 the generator protection zone after the generator breakeropened, a fact not recognized prior to the IEEE study. Thisphenomenon occurs during the seconds (not cycles) it takesfor the generator field to decay under ground fault conditions.

The working group’s approach was to investigate anddevelop different methods of protecting the generator whilepermitting a low-resistance grounded external system asdesigned. The results clearly revealed that Hybrid HighResistance Ground (HHRG) technology from EatonCorporation was the best overall solution.

HHRG — The Ultimate Solutionfor Generator Protection

An HHRG system consists of both low-resistance groundingas required by the external power system, as well as high-resistance grounding for the generator itself. Under externalground faults, the system is low-resistance grounded. Underinternal ground faults, the low-resistance ground source isquickly tripped offline, leaving the faulted generator to behigh-resistance grounded only.

In some systems, the external ground fault current available tofeed into the faulted generator can also cause excessive gen-erator damage. Such systems require a redesign of the groundfault protection system with significantly less available groundfault current. Eaton - Electrical Services & Systems (E-ESS)engineers are well qualified to make this evaluation and design

 the necessary changes.

Other Ways to Protect

Your AssetsEaton offers a comprehensive collection of products and serv-ices to protect your generators and your bottom line. Theseinclude partial discharge monitoring, static excitation retrofits,special generator breaker replacements, digital relay protec-

 tion modernization, turnkey installation, and ongoing mainte-nance and engineering services. E-ESS takes the burden offyour shoulders so you can focus on what you do best.

Partial discharge technology is an excellent tool to predictwhen a generator insulation system will fail. CombiningHHRG with the InsulGard Predictive Relay (partial discharge

 technology) for continuous partial discharge monitoring affordsyou a significant risk reduction and improvement in generatorsystem reliability.

Can Your Facility Benefitfrom HHRG?

Virtually any power system with medium voltage generatorscan reap benefits from installing an HHRG system. If any of thefollowing types of generators are installed in your facility, it isalmost certainly a candidate for HHRG:

Medium voltage generators Critical medium voltage emergency generators Low-resistance grounded generators Steam, gas turbine, diesel or hydro generators

Quite frequently, a generator that has experienced a major

fault where high ground fault current is available must bereturned to the factory for repair. You are left footing the bill foryour insurance deductible, as well as replacement power off

 the utility grid, demand charges, power factor penalties andlost production costs. The average repair time for these typesof catastrophic failures can last as long as four months. HHRGminimizes or eliminates these bills entirely by protecting thegenerator and greatly minimizing damage.

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Power SystemsEngineering Solution

E-ESS offers a total generator protection solution, including:

Hybrid high-resistance ground unit Grounding protection system redesign study Turnkey digital protective relay modernization and settings Integrated partial discharge system (InsulGard)

Field installation, startup and commissioning of equipment Instant Response Center for 24/7 monitoring Integrated project solution (turnkey)

Return on Investment

The total return on investment (ROI) is a function of the repaircosts, purchased replacement power for the extended repaircycle, and other costs such as disruption and inefficiencies to

 the steam cycle process. The following is an example.

40 MVA/32 MW steam turbine generator — operating 24/7 —loaded at 30 MW

Four cents/kWh rate from utility, $3/kWD, PF penalty < 0.95 200 ampere grounding resistor on the generator and a total

of 2200 amperes total ground fault current available in the system

Assume a ground fault occurs in the generator Four months factory repair time for total rewind (low-resistance

grounding only); three weeks partial field rewind for HHRG

© 2004 Eaton CorporationAll Rights ReservedPrinted in USAPublication No. SA02703007E / Z2701July 2004

Eaton Electrical Inc.1000 Cherrington ParkwayMoon Township, PA 15108United States tel: 1-800-525-2000www.EatonElectrical.com

For further information, please visit our Web site at:

www.EatonElectrical.com and click on Support, then Services &

Systems, or contact your nearest Eaton - Electrical Services &

Systems office.

For emergency service, call 1-800-498-2678 and ask for the office

nearest you.

Integrated Solution Summary

Asset Optimization Knowledge Management Integrated Project Solutions

Power Systems Engineering Solutions Power Systems Modernization New Equipment Services Field Services

Generator Conven- HHRG + PD HHRG+PD+Grounding  tional LRG System Changes

HHRG + PD TK Cost $0.0 $85K $85K

Grounding Study — ReduceTotal Ground Fault Current

 to Less than 1000 Amperes(not always required) N/A N/A $15K

System Ground DesignChanges (not always required) N/A N/A $50K

Generator Repair $1.0MDeductible

$1.8M Total(at factory) $400K (on-site) $250K (on-site)

Replacement kWh $3460K $865K $648K  (4 months)  (4 weeks)  (3 weeks) 

kWD Increase $360K $90K $67.5K

PF Penalty $262K $65.5K $37.5K

Steam Loss/Inefficiencies $200K $50K $37.5K

Insurance Premium Savings N/A Variable Variable

Sub-Total $5082K $1555.5K $1190.5K

Difference N/A $3526.5K $3891.5K

ROI N/A $3526.5K/$85K = 41X- $3891.5K/$85K = 46X-(Return on Investment) Equipment will pay Equipment will pay

for itself at least for itself at least41X at the first 46X at the firstgenerator ground generator groundfault occurrence. fault occurrence.

 

A Case Study in Savings

Application of HHRG technology helps cut costs and resultsin a quick payback through the following:

Significantly reduced internal generator damage frominternal ground faults

Reduction of available fault energy to less than 5%,depending on the system

On-site generator repair eliminates sending it back to the factory

Possible reduction in insurance premiums Avoidance of purchasing replacement power

(kWD, kWh, PF penalty, etc.) Elimination of steam, heat and process inefficiencies

during bypass around generator turbine