4
High-Voltage
Switching Equipment
4.1 Ambient Conditions .......................................................... 4-1
4.2 Disconnect Switches........................................................... 4-1
4.3 Load Break Switches .......................................................... 4-2
4.4 High-Speed Grounding Switches ...................................... 4-2
4.5 Power Fuses......................................................................... 4-3
4.6 Circuit Switchers ................................................................ 4-3
4.7 Circuit Breakers .................................................................. 4-4
4.8 GIS Substations .................................................................. 4-6
David L. Harris 4.9 Environmental Concerns ................................................... 4-6
Waukesha Electric Systems References ...................................................................................... 4-6
The design of the high-voltage substation must include consideration for the safe operation and main-
tenance of the equipment. Switching equipment is used to provide isolation, no load switching, load
switching, and/or interruption of fault currents. The magnitude and duration of the load and fault
currents will be significant in the selection of the equipment used.
System operations and maintenance must also be considered when equipment is selected. One signif-
icant choice is the decision of single-phase or three-phase operation. High-voltage power systems are
generally operated as a three-phase system, and the imbalance that will occur when operating equipment
in a single-phase mode must be considered.
4.1 Ambient Conditions
Air-insulated high-voltage electrical equipment is generally covered by standards based on assumed
ambient temperatures and altitudes. Ambient temperatures are generally rated over a range from –40°C to
+40°C for equipment that is air insulated and dependent on ambient cooling. Altitudes above 1000 meters
(3300 feet) may require derating.
At higher altitudes, air density decreases, hence the dielectric strength is also reduced and derating of
the equipment is recommended. Operating (strike distances) clearances must be increased to compensate
for the reduction in dielectric strength of the ambient air. Also, current ratings generally decrease at
higher elevations due to the decreased density of the ambient air, which is the cooling medium used for
dissipation of the heat generated by the load losses associated with load current levels.
4.2 Disconnect Switches
A disconnect switch is a mechanical device used to change connections within a circuit or isolate a circuit
from its power source, and is normally used to provide isolation of the substation equipment for
0-8493-1703-7/03/$0.00+$1.50
© 2003 by CRC Press LLC 4-1
© 2003 by CRC Press LLC
, 4-2 Electric Power Substations Engineering
maintenance. Typically a disconnect switch would be installed on each side of a piece of equipment to
provide a visible confirmation that the power conductors have been opened for personnel safety. Once
the switches are placed in the open position, safety grounds can be attached to the de-energized equipment
for worker protection. Switches can be equipped with grounding blades to perform the safety grounding
function.
Disconnect switches are designed to continuously carry load currents and momentarily carry higher
capacity for short-circuit currents for a specified duration (typically specified in seconds). They are
designed for no load switching, opening or closing circuits where negligible currents are made or
interrupted, or when there is no significant voltage across the open terminals of the switch. They are
relatively slow-speed operating devices and therefore are not designed for arc interruption. Disconnect
switches are also installed to bypass breakers or other equipment for maintenance and can also be used
for bus sectionalizing. Interlocking equipment is available to prevent inadvertent operating sequence by
inhibiting operation of the disconnect switch operation until the fault and/or load currents have been
interrupted by the appropriate equipment.
Single-phase or three-phase operation is possible for some switches. Operating mechanisms are nor-
mally installed to permit operation of the disconnect switch by an operator standing at ground level.
The operating mechanisms provide a swing arm or gearing to permit operation with reasonable effort
by utility personnel. Motor operating mechanisms are also available and are applied when remote
switching is necessary.
Disconnect switch operation can be designed for vertical or horizontal operating of the switch blades.
Several configurations are frequently used for switch applications including:
• Vertical break
• Double break switches
• V switches
• Center break switches
• Hook stick switches
• Vertical reach switches
• Grounding switches
Phase spacing is usually adjusted to satisfy the spacing of the bus system installed in the substation.
4.3 Load Break Switches
A load break switch is a disconnect switch that has been designed to provide making or breaking of
specified currents. This is accomplished by addition of equipment that increases the operating speed of
the disconnect switch blade and the addition of some type of equipment to alter the arcing phenomena
and allow the safe interruption of the arc resulting when switching load currents.
Disconnect switches can be supplied with equipment to provide a limited load switching capability.
Arcing horns, whips, and spring actuators are typical at lower voltages. These switches are used to
de-energize or energize a circuit that possesses some limited amount of magnetic or capacitive current,
such as transformer exciting current or line charging currents.
An air switch can be modified to include a series interrupter (typically vacuum or SF6) for higher
voltage and current interrupting levels. These interrupters increase the load break capability of the
disconnect switch and can be applied for switching load or fault currents of the associated equipment.
4.4 High-Speed Grounding Switches
Automatic high-speed grounding switches are applied for protection of transformer banks when the cost
of supplying other protective equipment is too costly. The switches are generally actuated by discharging
a spring mechanism to provide the “high-speed” operation. The grounding switch operates to provide
© 2003 by CRC Press LLC
High-Voltage
Switching Equipment
4.1 Ambient Conditions .......................................................... 4-1
4.2 Disconnect Switches........................................................... 4-1
4.3 Load Break Switches .......................................................... 4-2
4.4 High-Speed Grounding Switches ...................................... 4-2
4.5 Power Fuses......................................................................... 4-3
4.6 Circuit Switchers ................................................................ 4-3
4.7 Circuit Breakers .................................................................. 4-4
4.8 GIS Substations .................................................................. 4-6
David L. Harris 4.9 Environmental Concerns ................................................... 4-6
Waukesha Electric Systems References ...................................................................................... 4-6
The design of the high-voltage substation must include consideration for the safe operation and main-
tenance of the equipment. Switching equipment is used to provide isolation, no load switching, load
switching, and/or interruption of fault currents. The magnitude and duration of the load and fault
currents will be significant in the selection of the equipment used.
System operations and maintenance must also be considered when equipment is selected. One signif-
icant choice is the decision of single-phase or three-phase operation. High-voltage power systems are
generally operated as a three-phase system, and the imbalance that will occur when operating equipment
in a single-phase mode must be considered.
4.1 Ambient Conditions
Air-insulated high-voltage electrical equipment is generally covered by standards based on assumed
ambient temperatures and altitudes. Ambient temperatures are generally rated over a range from –40°C to
+40°C for equipment that is air insulated and dependent on ambient cooling. Altitudes above 1000 meters
(3300 feet) may require derating.
At higher altitudes, air density decreases, hence the dielectric strength is also reduced and derating of
the equipment is recommended. Operating (strike distances) clearances must be increased to compensate
for the reduction in dielectric strength of the ambient air. Also, current ratings generally decrease at
higher elevations due to the decreased density of the ambient air, which is the cooling medium used for
dissipation of the heat generated by the load losses associated with load current levels.
4.2 Disconnect Switches
A disconnect switch is a mechanical device used to change connections within a circuit or isolate a circuit
from its power source, and is normally used to provide isolation of the substation equipment for
0-8493-1703-7/03/$0.00+$1.50
© 2003 by CRC Press LLC 4-1
© 2003 by CRC Press LLC
, 4-2 Electric Power Substations Engineering
maintenance. Typically a disconnect switch would be installed on each side of a piece of equipment to
provide a visible confirmation that the power conductors have been opened for personnel safety. Once
the switches are placed in the open position, safety grounds can be attached to the de-energized equipment
for worker protection. Switches can be equipped with grounding blades to perform the safety grounding
function.
Disconnect switches are designed to continuously carry load currents and momentarily carry higher
capacity for short-circuit currents for a specified duration (typically specified in seconds). They are
designed for no load switching, opening or closing circuits where negligible currents are made or
interrupted, or when there is no significant voltage across the open terminals of the switch. They are
relatively slow-speed operating devices and therefore are not designed for arc interruption. Disconnect
switches are also installed to bypass breakers or other equipment for maintenance and can also be used
for bus sectionalizing. Interlocking equipment is available to prevent inadvertent operating sequence by
inhibiting operation of the disconnect switch operation until the fault and/or load currents have been
interrupted by the appropriate equipment.
Single-phase or three-phase operation is possible for some switches. Operating mechanisms are nor-
mally installed to permit operation of the disconnect switch by an operator standing at ground level.
The operating mechanisms provide a swing arm or gearing to permit operation with reasonable effort
by utility personnel. Motor operating mechanisms are also available and are applied when remote
switching is necessary.
Disconnect switch operation can be designed for vertical or horizontal operating of the switch blades.
Several configurations are frequently used for switch applications including:
• Vertical break
• Double break switches
• V switches
• Center break switches
• Hook stick switches
• Vertical reach switches
• Grounding switches
Phase spacing is usually adjusted to satisfy the spacing of the bus system installed in the substation.
4.3 Load Break Switches
A load break switch is a disconnect switch that has been designed to provide making or breaking of
specified currents. This is accomplished by addition of equipment that increases the operating speed of
the disconnect switch blade and the addition of some type of equipment to alter the arcing phenomena
and allow the safe interruption of the arc resulting when switching load currents.
Disconnect switches can be supplied with equipment to provide a limited load switching capability.
Arcing horns, whips, and spring actuators are typical at lower voltages. These switches are used to
de-energize or energize a circuit that possesses some limited amount of magnetic or capacitive current,
such as transformer exciting current or line charging currents.
An air switch can be modified to include a series interrupter (typically vacuum or SF6) for higher
voltage and current interrupting levels. These interrupters increase the load break capability of the
disconnect switch and can be applied for switching load or fault currents of the associated equipment.
4.4 High-Speed Grounding Switches
Automatic high-speed grounding switches are applied for protection of transformer banks when the cost
of supplying other protective equipment is too costly. The switches are generally actuated by discharging
a spring mechanism to provide the “high-speed” operation. The grounding switch operates to provide
© 2003 by CRC Press LLC
