Appendix II - Glossary

Revised: October 2020

AMMETER

An indicating device that shows the amount of current flow on a particular piece of equipment such as a breaker or transformer. There are two types of indicating ammeters: instantaneous reading and maximum demand reading.

ARCING HORN

An additional length of smaller conductor connected to the end of a solid blade switch to protect the end of the disconnect from pitting when opening and closing.

AUTO-BOOSTER

A single-phase line voltage regulating auto-transformer. The four-step regulators (5% or 10%) can only raise or lower the load voltage, dependent on their connection.

AUTOMATIC TRANSFER SCHEME

A switch or set of switches that automatically operate the transmission or distribution system according to input received from potential-sensing devices on the line or station bus.

BREAKER FAILURE RELAY

A relay that is used as back up protection if a breaker fails to operate to clear a fault.

BUSHING, FEED THROUGH

A device used on the underground distribution system to connect two elbows for the purpose of feeding primary current through them; or, the connection of a separate ground source to a de-energized conductor.

BUSHING, PARKING

An insulating device used on the underground distribution system to isolate an elbow so that no current can flow through it.

BUS, MAIN

The principal group of conductors (usually rigid) that serves as a common connection between two or more circuits in a substation, interconnecting equipment of the same voltage.

BUS TIE SWITCH

A switch that separates two sections of a bus, for example, the two main buses of a two-bank station.

BUS TIE BREAKER

A breaker that separates two sections of a bus, for example, the two main buses of a two-bank station.

BUS, TRANSFER

A group of conductors (usually rigid) that serves as an alternate connection between two or more circuits in a substation. Used when transferring load between two circuits, it can be energized only when a circuit breaker or set of transfer disconnects is closed.

BUS TRANSFER SWITCH OR DISCONNECT

A switch or disconnect that transfers load to a different source through the transfer bus.

BYPASS DISCONNECT

A set of disconnects used to parallel the current around a device such as a regulator, sectionalizer, or recloser. The device can then be opened without dropping load current or load.

CAPACITOR BANK

A set of capacitors connected to the primary line or station bus to improve the system power factor or voltage.

CAPACITOR DISCONNECT

A solid blade, non-load interrupting device used to isolate a capacitor bank after the current has been interrupted by a load interrupting device.

CAPACITOR FUSE

A protective device that operates during overcurrents and fault situations within a capacitor bank. They may be used as the isolating point for the capacitor bank if no capacitor disconnects are available.

CHARGING CURRENT

The amount of current that flows into a line, cable, or piece of electrical equipment that is energized, but has no load connection.

CIRCUIT BREAKER

A switching device that can interrupt a circuit in a power system under over-load or fault (short circuit) conditions, usually automatically tripped by protective relays. The circuit breaker can also be operated by SCADA or local control to interrupt normal load currents.

CIRCUIT BREAKER, MAIN

The circuit breaker and associated disconnects between the low side of a substation transformer and the main bus.

CIRCUIT SWITCHER

A motor-operated SF6-filled transmission switch with load and fault interrupting capability. The disconnects open automatically after the load or fault current has been interrupted in the SF6.

CLEARANCE

“The certification by the proper authority that a specified line, cable or station is de-energized, that the proper precautionary measures have been taken and the line, cable or station is being turned over to the employee.” Formal, recorded permission by the System Operator for the employee(s) to work on a particular line, cable or station that has been identified, isolated, de-energized, and tagged with a Master Safety Card(s).

CLEARANCE, FIELD

A procedure that allows employees to establish clearance(s) on lines, cables or stations not under the control of the Energy Control Center.

CLEARANCE POINT

A primary device under the control of the ECC that shall be cleared and tagged for an employee.

CLEARANCE, POINT OF

A point to allow the employee to establish a Field Clearance when the end of the line is not under the control of the ECC.

CLEARANCE, TERMINAL

The procedure whereby a switch or terminal is cleared and tagged for a foreign utility Dispatcher or District Generation LO/TO Coordinator. For example: A District generation facility wishes to work on a section of their line that is fed by the District. The District employee will be requested to open the source switch and tag for the Generation LO/TO Coordinator with a Master Safety Card(s).

CLEARED

A term referring to lines, equipment or stations which have been de-energized by providing visible air breaks to all possible sources of feed. Must be treated as energized until a clearance has been issued.

CREW (SUBSTATION OR LINE)

Two or more electrical employees assembled to construct, maintain, or repair lines, cables or stations.

CURRENT LIMITING FUSE

A fuse that, when melted by current within its current limiting range, produces a high resistance, which reduces the current’s magnitude and duration.

CURRENT TRANSFORMERS (CT)

A transformer used to step down current values to an amount suitable for use in metering and relays.

CVR (CONSERVATION VOLTAGE REDUCTION)

Lowered tap changer control voltages to achieve lower power consumption.

DEAD FRONT

A piece of electrical equipment with no exposed energized parts or conductors over 600 volts.

DE-COUPLED LINKAGE

To disconnect the operating mechanism and motor from the operating linkage of a motor-operated switch, preventing the inadvertent operation of the switch.

DE-ENERGIZED (NO LOAD) TAP CHANGER

A device for changing the taps of an apparatus only when the apparatus is de-energized.

DIFFERENTIAL RELAY

A protective relay that measures the current flowing into and out of a transformer or bus section. When the currents are not matched, or not within certain parameters, the relay will operate to isolate the device.

DIRECTIONAL RELAY

A protective relay (overcurrent, ground, and distance) that allows for the opening of the protected device only when the over-current is flowing in a pre-determined direction.

DISCONNECT SWITCH

A mechanism used to open or close a circuit. Disconnect switches can be manual or motor-operated.

Types of disconnect switches:

• Load or Line Disconnects—The disconnects to the load or line side of a switch or device.
• Source Disconnects—The disconnects to the source side of a switch or device.

DISTANCE RELAY (IMPEDANCE OR ZONE)

A relay used exclusively on the transmission system that operates for phase-to-phase faults, due to the change in impedance of a line during fault conditions. It is directionally controlled and can have up to three zones of protection.

ELBOW, LOAD BREAK

A connecting point on the underground distribution system between the primary cable and a piece of equipment that can be operated under normal load.

ELBOW, NON-LOAD BREAK/ DEAD BREAK

A connecting point on the underground distribution system between the primary cable and a piece of equipment that cannot be operated under load.

EMPLOYEE

An employee who is familiar with the construction and operation of lines and/or equipment that concerns his/her position and who is fully aware of the hazards connected therewith; or, one who has passed a journey status examination for the particular branch of the electrical trades with which he/she may be connected.

FAULT

• A short circuit between conductors or between conductors and ground which can cause an abnormal current flow.
• The breaking of conductors or the point of failure which causes an outage on a line, piece of equipment, or station.

FAULT INDICATOR

A device on the electrical system that shows if fault current has flowed through a given point.

FEEDER

A three-phase primary line that supplies the distribution load from the substation to the transformers. Feeders normally have alternate sources from other distribution substations.

FEEDER TIE

A normally open switch usually outside the substation that separates two feeders, for example, two feeders from different substation banks.

FEED THROUGH BUSHING

A device used on the underground distribution system to connect two elbows for the purpose of feeding primary current through them; or, the connection of a separate ground source to a de-energized conductor.

FIELD CLEARANCE

A procedure that allows employees to establish clearance(s) on lines, cables or stations not under the control of the Energy Control Center.

FOREIGN UTILITY

A utility that has inter-tie capabilities with the District’s electric system.

FUSE, CURRENT LIMITING

A fuse that, when melted by current within it’s current limiting range, produces a high resistance, which reduces the current’s magnitude and duration.

FUSE DISCONNECT

A disconnect with a fusible element that opens when a predetermined amount of load or fault current passes through it and can also be opened manually under normal load conditions.

FUSE, HIGH-SIDE

An individual phase overcurrent or fault current protective device on the high voltage side of a distribution substation transformer.

GANG OPERATED SWITCH

A three-phase switch operated by a handle. All three phases are connected by a common linkage, and open or close simultaneously.

GET-AWAY SWITCH

The three-phase primary feed from a substation circuit breaker out of the substation to the first point of disconnection (get-away switch) from the power system. “Get-away” switches can be overhead line disconnects or underground padmount switches.

GROUND

A conducting connection whether intentional or accidental, between an electric circuit or equipment and the earth, or to some conducting body that serves in place of the earth.

GROUND OVERCURRENT RELAY

A protective relay that responds primarily to system neutral or ground faults. This relay can also detect large unbalanced load currents on a three-phase system.

GROUND, PERSONAL PROTECTIVE

Temporary protective grounds placed on a line, cable, or equipment to prevent each employee from being exposed to hazardous differences in electrical potential.

GROUND SWITCH

A permanently mounted switch on a line, capacitor, or a piece of equipment that, when closed, grounds the device. Ground switches are to be closed only after all means of energization have been opened and isolated.

HIGH-SIDE FUSE

An individual phase overcurrent or fault current protective device on the high voltage side of a distribution substation transformer.

HIGH-SIDE SWITCH

A manually operated visible air break switch on the high voltage side of a station transformer, with arcing horns to drop the bank charging currents.

HOT LINE HOLD

A safety tag issued to the foreman in charge when working on energized distribution lines. When Hot Line Hold is enabled, breakers and/or reclosers upstream of the work location are set to non-reclose and instantaneous trip.

HOT LOG

A written log used and maintained by the System Operator to document any switching and clearance steps not performed on a switching order.

INRUSH CURRENT

A short duration, large value current required to initially magnetize the core of a transformer.

INSULATOR

A non-conductive support for a conductor. It inhibits the flow of current from the conductor to earth or to another conductor.

J-BOX

A junction device on the underground distribution system that connects multiple elbows so that primary current can flow through them.

LATERAL

A circuit with one source of feed which can be one, two or three phase.

LIGHTNING ARRESTOR

A device designed to protect electric equipment from high transient voltage by diverting to earth a momentary high voltage surge. Usually found on substation transformers on the high and low sides, and on underground cable terminations.

LIVE FRONT

A piece of electrical equipment with exposed parts or conductors energized over 600 Volts.

LOAD BREAK ELBOW

A connecting point on the underground distribution system between the primary cable and a piece of equipment that can be operated under normal load.

LOAD BUST TOOL

A tool for opening disconnects under normal load conditions. The disconnect(s) must be equipped with hooks to accommodate this tool.

LOAD INTERRUPTER

A switching device that can be opened under normal load conditions. It can safely interrupt current up to its nameplate rating.

LOAD TAP CHANGING TRANSFORMER (LTC)

A station transformer that, under load, can vary the output windings of the secondary for voltage control. The tap changing compartment is part of the entire transformer enclosure,and shall not be taken out of service until all load has been transferred from the transformer, and the transformer has been de-energized.

LOCAL/REMOTE SWITCH

A switch at the device used to enable or disable supervisory control.

LOCKOUT (BREAKER)

The final cycle of a station circuit breaker, line recloser, sectionalizer, etc., that opens and remains open during a fault after going through its predetermined operations.

LOCKOUT RELAY (86 DEVICE)

A device that shuts down or holds equipment out of service when abnormal conditions occur. Substation/Generation employee shall manually reset it before the equipment can be placed back in service.

LOCKOUT/ TAGOUT (LO/TO)

A procedure of installing cards and locks used to provide employees safety by isolating a stored energy source.

LOOP FEED

A line that can be fed from more than one source. Can consist of one, two, or three phases.

MAIN BUS

The principal group of conductors (usually rigid) that serves as a common connection between two or more circuits in a substation, interconnecting equipment of the same voltage.

MAIN CIRCUIT BREAKER

The circuit breaker and associated disconnects between the low side of a substation transformer and the main bus.

MOTOR OPERATED SWITCH

A switch that is opened and closed by an electric motor.

NEUTRAL POSITION (VOLTAGE CONTROL DEVICE)

The point on a voltage regulator, LTC, or auto-booster where no difference in voltage exists between the load and source sides. This is the only position in which a voltage regulating device shall be bypassed while it is energized.

NEUTRAL REACTOR

A large coil connected between the neutral bushing of a wye-connected substation transformer and ground. It limits the amount of fault current that flows through the transformer when a close-in ground fault occurs.

NON-LOAD BREAK ELBOW

A connecting point on the underground distribution system between the primary cable and a piece of equipment that cannot be operated under load.

PARALLEL

Two or more lines running side by side for a distance.

PARALLELING

Two or more lines or pieces of equipment that are connected to the same bus or load.

PARKING BUSHING

An insulating device used on the underground distribution system to isolate an elbow so that no current can flow through it.

PERSONAL PROTECTIVE GROUND

Temporary protective grounds placed on a line, cable or equipment to prevent each employee from being exposed to hazardous differences in electrical potential.

PHASE OVERCURRENT RELAY

A protective relay that operates when the current through it is equal to or greater than its setting. Overcurrent relays are usually a combination of instantaneous and time delay units.

POTENTIAL TRANSFORMER (PT)

A transformer used to step down primary voltage to a low voltage (usually 120) for use in metering and relays.

POWER TRANSFORMER

A transformer used to change the voltage level for power transmission or distribution. A step-up transformer increases the voltage; a step down transformer decreases the voltage.

PRIMARY DISTRIBUTION VOLTAGE

The voltage at which electricity is delivered from the distribution substation to the consumer’s transformer. The District’s primary distribution voltage is typically 12kV.

QUALIFIED PERSON, QUALIFIED EMPLOYEE OR QUALIFIED SUPERVISOR

An employee or supervisor who is familiar with the construction and operation of lines and/or equipment that concerns his/her position and who is fully aware of the hazards connected therewith, or, one who has passed a journey status examination for the particular branch of the electrical trades with which he/she may be connected.

RADIAL

A line fed from one direction, with no other means of tying to another source. The line can be one, two, or three phase.

RECLOSER

An automatic load or fault interrupter that opens when a predetermined amount of current flows, and can be set to reclose a number of times to test the line. If the fault or overload still exists after attempting the preset number of recloses, the recloser will stay open until it has been manually reset. This device can be single or three phase.

RECLOSING OR NON-RECLOSING CUTOUT SWITCH

A switch that opens the reclosing circuit and prevents a circuit breaker or recloser from going through its automatic reclose cycle.

RECLOSING RELAY

A programming relay that will automatically reclose a Circuit Breaker after it has tripped open. The relay can be set to reclose the breaker multiple times. If the fault or overload still exists after attempting the preset number of recloses, the relay will lock open and block further automatic attempts to reclose.

RELAY, BREAKER FAILURE

A relay that is used as back up protection if a breaker fails to operate to clear a fault.

RELAY, DIFFERENTIAL

A protective relay that measures the current flowing into and out of a transformer or bus section. When the currents are not matched, or not within certain parameters, the relay will operate to isolate the device.

RELAY, DIRECTIONAL

A protective relay (overcurrent, ground, and distance) that will allow for the opening of the protected device only when the over-current is flowing in a pre-determined direction.

RELAY, DISTANCE (IMPEDANCE OR ZONE)

A relay used exclusively on the transmission system that operates for phase-to-phase faults, due to the change in impedance of a line during fault conditions. It is directionally controlled and can have up to three zones of protection.

RELAY, GROUND OVERCURRENT

A protective relay that responds primarily to system neutral or ground faults. This relay can also detect large unbalanced load currents on a three-phase system.

RELAY, LOCKOUT (86 DEVICE)

A device that shuts down or holds equipment out of service when abnormal conditions occur. Substation/Jackson employee shall manually reset it before the equipment can be placed back in service.

RELAY, PHASE OVERCURRENT

A protective relay that operates when the current through it is equal to or greater than its setting. Overcurrent relays are usually a combination of instantaneous and time delay units.

RELAY, RECLOSING

A programming relay that will automatically reclose a Circuit Breaker after it has tripped open. The relay can be set to reclose the breaker multiple times. If the fault or overload still exists after attempting the preset number of recloses, the relay will lock open and block further automatic attempts to reclose.

RELAY, UNDERFREQUENCY

A relay that operates at a preset frequency value; usually associated with load shedding schemes to maintain system frequency.

SCADA

(Supervisory Control and Data Acquisition) A computer system that the System Operators use to remotely monitor and control the power distribution throughout the service area. SCADA also provides for the remote monitoring and control of the Jackson Hydroelectric Project and SCADA data (i.e. System load) that is used by others within the District such as power scheduling and system planning.

SECONDARY VOLTAGE

The voltage that PUD supplies to the consumer from the low voltage side of the distribution transformer, usually in the range of 120 volts to 480 volts.

SECTIONALIZE

To divide lines, cables, or substation bus into sections.

SECTIONALIZER

A fault isolating device that shall be used with an automatic line recloser or circuit breaker. The sectionalizer opens on a de-energized line after counting a predetermined number of overcurrent interruptions on the source protective device. Sectionalizers do not have fault interrupting capability, but can interrupt load up to their continuous current rating. This device can be single or three phase.

SOLID BLADE DISCONNECT

A manual unfused device that opens or closes a circuit.

STACKED ELBOWS (HAMMERHEADS)

A connection point on the primary underground distribution system. Stacked elbows shall be de-energized to be separated. (See Elbow, Non-Load Break/Dead Break.)

STATION SERVICE TRANSFORMER

A distribution transformer used within a substation to step down primary voltage to 120 or 240 volts for station lighting, battery chargers, etc.

SUPERVISORY CONTROL (SCADA)

The ability to operate a device from a remote location such as the Energy Control Center. (See SCADA.)

SURGE ARRESTOR

A device designed to protect electric equipment from high-transient voltage by diverting to earth a momentary high-voltage surge. Usually found on substation transformers on the high and low sides, and on underground cable terminations.

SWITCH

A device for making or breaking an electric circuit.

SWITCH CABINET

A switching and/or isolating point on the underground primary distribution system. Switch cabinets may contain manually operated disconnects (single blade or gang operated), fusible elements, or any combination of both.

SWITCH, GANG-OPERATED

A three-phase switch operated by a handle. All three phases are connected by a common linkage, and open or close simultaneously.

SWITCH, GROUND

A permanently mounted switch on a line, capacitor, or a piece of equipment that, when closed, grounds the device. Ground switches are to be closed only after all means of energization have been opened and isolated.

SWITCH, HIGH-SIDE

A manually operated visible air break switch on the high voltage side of a station transformer, with arcing horns to drop the bank charging currents.

SWITCHING ORDERS

Detailed instructions to perform switching operations in a specific sequence.

SWITCHING SETTINGS

Alternate tap changer adjustments used when the distribution system is in an abnormal configuration.

SWITCH, LOCAL/REMOTE

A switch at the device used to enable or disable supervisory control.

SYSTEM OPERATOR

An employee who has authority over switching and clearances on lines, cables, stations and equipment for the District’s electric system.

TARGETS (EQUIPMENT)

A visual display that indicates the status of a device.

TERMINAL CLEARANCE

The procedure whereby a switch or terminal is cleared and tagged for a Foreign Utility Dispatcher. (For example: A generation facility wishes to work on a section of their line that is fed by the District. The District employee will be requested to open the source switch and tag for the Foreign Utility Dispatcher with a Master Safety Card.)

TRANSFER BUS

A group of conductors (usually rigid) that serves as an alternate connection between two or more circuits in a substation. Used when transferring load between two circuits; it can be energized only when a circuit breaker or set of transfer disconnects is closed.

TRANSFORMER, LOAD TAP CHANGING (LTC)

A station transformer that, under load, can vary the output windings of the secondary for voltage control. The tap changing compartment is part of the entire transformer enclosure, and shall not be taken out of service until all load has been transferred from the transformer, and the transformer has been de-energized.

TRANSFORMER BANK DISCONNECT OR “MAIN” BREAKER

The isolating point on the distribution side of a substation transformer, between the transformer and the main bus.

TRANSFORMER, POTENTIAL (PT)

A transformer used to step down primary voltage to low voltage (usually 120) for use in metering and relays.

TRANSFORMER, POWER

A transformer used to change the voltage level for power transmission or distribution. A step-up transformer increases the voltage; a step down transformer decreases the voltage.

TRANSFORMERS, CURRENT (CT)

A transformer used to step down current values to an amount suitable for use in metering and relays.

TRANSFORMER, STATION SERVICE

A distribution transformer used within a substation to step down primary voltage to 120 or 240 volts for station lighting, battery chargers, etc.

UNDERFREQUENCY RELAY

A relay that operates at a preset frequency value; usually associated with load shedding schemes to maintain system frequency.

VOLTAGE REGULATOR

A device used to automatically maintain a predetermined voltage level in distribution substations and on distribution lines.