Medium Voltage Application Guide
Medium Voltage Application Guide
Medium Voltage Application Guide
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Incomer feeder<br />
panel<br />
Transformer<br />
Motor<br />
Power factor<br />
bank<br />
SWITCHGEAR<br />
ANSI protection codes<br />
The American National Standards Institute developed a standardised table of numerical codes indicating specific<br />
protection functions. These codes are internationally recognised, and are often used in single line diagrams or<br />
tender documents as part of a project specification.<br />
ANSI codes commonly specified for medium voltage feeders, transformers, motor and power factor banks.<br />
ANSI<br />
code<br />
Function Description <strong>Application</strong> Components<br />
required<br />
CT VT<br />
24 Volts per hertz<br />
relay<br />
25 Synchronising or<br />
synch-check<br />
device<br />
26 Apparatus<br />
device<br />
27 Undervoltage<br />
relay<br />
37 Undercurrent/<br />
power relay<br />
38 Bearing<br />
protective<br />
device<br />
46 Phase reversal or<br />
current<br />
imbalance relay<br />
47 Phase sequence<br />
voltage relay<br />
48 Incomplete<br />
sequence relay<br />
49<br />
(P,R)<br />
50<br />
(N,G)<br />
51<br />
(N,G)<br />
Machine or<br />
transformer<br />
thermal relay<br />
AC<br />
instantaneous or<br />
di/dt relay<br />
AC<br />
time-overcurren<br />
t relay<br />
59 Overvoltage<br />
relay<br />
64 Ground (earth)<br />
detector relay<br />
Activates if the Volts/Hertz ratio falls<br />
outside a preset range.<br />
Operates when the voltage, frequency,<br />
and phase angles between two AC<br />
systems are within a preset acceptable<br />
range.<br />
Activates if the monitored apparatus<br />
exceeds a preset temperature.<br />
Activates if the voltage falls below a preset<br />
level.<br />
Activates if the current or power falls<br />
below a preset level.<br />
Activates when the upper temperature<br />
limit of a machine bearing is exceeded or<br />
abnormal bearing wear is detected.<br />
Monitors line currents and activates when<br />
phase reversal is detected or when line<br />
current imbalance of negative phase<br />
sequence currents fall outside a preset<br />
range.<br />
Monitors line voltages and activates when<br />
phase reversal is detected.<br />
Trips or turns off a device if a particular<br />
sequence has not been completed within<br />
a preset time period.<br />
Activates if the monitored machine or<br />
transformer part exceeds a preset<br />
temperature.<br />
(P = PTC, R = RTD)<br />
Activates if the current or di/dt values<br />
exceed a preset level. Normally indicates a<br />
medium to high level fault condition.<br />
(N = neutral, G = ground)<br />
Activates when the current exceeds a<br />
preset level based on a thermal overload<br />
trip curve.<br />
(N = neutral, G = ground)<br />
Activates if the voltage exceeds a preset<br />
level.<br />
Activates when earth current flow is<br />
detected from the frame, chassis, case or<br />
structure of a device, indicating a<br />
breakdown of insulation in an electrical<br />
machine or transformer.<br />
X<br />
X<br />
X<br />
X<br />
X X X<br />
X X X X<br />
X X<br />
X<br />
X X X<br />
X<br />
X<br />
X<br />
X X X<br />
X X X X X<br />
X X X X X<br />
X X X X<br />
X X X<br />
710-12280-00A <strong>Medium</strong> <strong>Voltage</strong> <strong>Application</strong> <strong>Guide</strong> Page 125
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