Capacitor Bank Protection for Simple and Complex Configurations
Capacitor Bank Protection for Simple and Complex Configurations
Capacitor Bank Protection for Simple and Complex Configurations
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<strong>Capacitor</strong> <strong>Bank</strong> <strong>Protection</strong> <strong>for</strong> <strong>Simple</strong><br />
<strong>and</strong> <strong>Complex</strong> <strong>Configurations</strong><br />
Roy Moxley, Jeff Pope, <strong>and</strong> Jordan Allen<br />
Schweitzer Engineering Laboratories, Inc.<br />
Copyright © SEL 2011
<strong>Capacitor</strong> <strong>Bank</strong>s Come in All Sizes
With <strong>and</strong> Without
Large <strong>and</strong> Small
This Paper Does Not Discuss<br />
Series <strong>Bank</strong>s
Units in<br />
Series<br />
Shunt <strong>Capacitor</strong> Nomenclature<br />
Units in Parallel<br />
<strong>Capacitor</strong><br />
Element<br />
<strong>Capacitor</strong><br />
Unit
Shunt <strong>Capacitor</strong> <strong>Bank</strong>s Provide…<br />
• Voltage support<br />
• Reactive power reserve<br />
• Power factor correction<br />
• Harmonic filtering
(a)<br />
Shunt <strong>Capacitor</strong> <strong>Bank</strong>s<br />
Common <strong>Configurations</strong><br />
Ungrounded<br />
Single Wye<br />
(b)<br />
Ungrounded Double Wye<br />
(neutrals may or may not<br />
be connected)
(c)<br />
Shunt <strong>Capacitor</strong> <strong>Bank</strong>s<br />
Common <strong>Configurations</strong><br />
Grounded Single Wye<br />
(d)<br />
Grounded Double Wye
Shunt <strong>Capacitor</strong> <strong>Bank</strong>s<br />
To Fuse or Not to Fuse?<br />
• Externally fused<br />
• Internally fused<br />
• Fuseless<br />
• Unfused
Per-Phase Voltage Differential<br />
Common Unbalance <strong>Protection</strong> Methods<br />
Busbars<br />
PT PT PT<br />
Relay<br />
(a) Voltage Differential <strong>Protection</strong>, Single Wye
Voltage Differential<br />
Common Unbalance <strong>Protection</strong> Methods<br />
Busbars<br />
Relay<br />
PT<br />
(c) Compensated Unbalance Method
Per-Phase Current <strong>Protection</strong><br />
Common Unbalance <strong>Protection</strong> Methods<br />
Busbars<br />
Relay<br />
(b) Phase Unbalance or H Bridge
Neutral Current or Voltage<br />
Ungrounded <strong>Bank</strong><br />
Busbars Busbars<br />
CT PT<br />
Relay<br />
(a) Neutral Current<br />
Unbalance<br />
Relay<br />
(b) Neutral Voltage<br />
Unbalance
Neutral Current Differential<br />
Grounded <strong>Bank</strong><br />
Busbars<br />
Relay<br />
(a) Current Differential <strong>Protection</strong>, Double Wye
Busbars<br />
Voltage Differential<br />
Grounded <strong>Bank</strong><br />
PT PT<br />
Relay<br />
(b) Voltage Differential <strong>Protection</strong>, Double Wye
Double Wye, <strong>Capacitor</strong> Grounded<br />
1.117<br />
1.117<br />
CT2<br />
IA<br />
IA<br />
0.001<br />
650.845 650.845<br />
1.117<br />
1.117<br />
PT2
Digitals<br />
I<br />
V<br />
Current More Sensitive<br />
Single Element Failure<br />
Current Jumps Noticeably<br />
Voltage Change Lost in Noise
Digitals<br />
Delta Voltage Barely Detectable<br />
Two Elements Failed<br />
I<br />
V<br />
Current<br />
Voltage Change Detectable<br />
Below Relay Threshold
Digitals<br />
Voltage Change Clear <strong>and</strong> Detectable<br />
Three Elements Failed<br />
I<br />
V<br />
Current <strong>and</strong> Voltage Jumps Similar
Double H <strong>Bank</strong><br />
More Measurements, More <strong>Complex</strong>ity<br />
150 0.0145<br />
483.311<br />
0.001<br />
483.311<br />
21.911<br />
0.001<br />
21.911
Digitals<br />
I<br />
V<br />
Internally Fused<br />
Very Small Changes<br />
Current at ~ 7 Times Minimum Pickup<br />
Voltage at ~ 0.1 Times Minimum Pickup
I<br />
V<br />
Unit Failure on Double H <strong>Bank</strong><br />
Fast Operation of Both<br />
Voltage <strong>and</strong> Current Elements
Resistor<br />
<strong>for</strong> Tuning<br />
CT3B IC1<br />
IC1<br />
CT3C IC2<br />
IC2<br />
5.018<br />
5.018<br />
28.85<br />
115.401<br />
Single Phase of<br />
C-Type <strong>Bank</strong><br />
Unit Capacitance
CT3B IC1<br />
IC1<br />
CT3C IC2<br />
IC2<br />
Exp<strong>and</strong> Units<br />
in Model<br />
8 Series Sections<br />
Per Unit<br />
3 Series Sections<br />
Per Unit
I<br />
V<br />
C-<strong>Bank</strong> Sensitivity<br />
One Element Failed on Main Leg<br />
Balance Current Twice Minimum Pickup<br />
Balance Voltage Half Minimum Pickup
Tougher to Protect Tuning Portion<br />
Two Elements Failed<br />
I<br />
V<br />
Current 2.5 Times Minimum Pickup<br />
Voltage 0.25 Times Minimum Pickup
Which Unit Failed?<br />
Fault Location Important in <strong>Capacitor</strong> <strong>Bank</strong>s<br />
Photo provided courtesy of Niagara Mohawk,<br />
a National Grid Company
Voltage Polarity Provides Failed<br />
Element Direction<br />
Positive Shift<br />
Negative Shift
Small Variations Do Not Have to Be<br />
Caused by Failed Units
Conclusions<br />
• Failure of even a<br />
single element is<br />
readily detectable in<br />
most banks<br />
• Current balance is<br />
generally more<br />
sensitive than<br />
voltage balance
Slightly Less Obvious Conclusions<br />
• Even though not as<br />
sensitive, voltage<br />
elements make great<br />
backup<br />
• Flexible logic allows<br />
capability of combining<br />
protection elements,<br />
counting failures, <strong>and</strong><br />
making protection<br />
adaptive
Any Questions?
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