Substation1
Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

wye-delta transformer
a connection of a three-phase transformer with one primary and one secondary which can be considered as three similar single-phase transformers. The primary is connected in wye, that is one terminal from each phase is connected to neutral and one to a line voltage. The secondary is connected in delta, with each phase connected between two line voltages.
wye-wye transformer
a three-phase transformer with both the primary and secondary coils connected in wye. This connection is considered undesirable, due to the triple harmonics in the exciting current. To maintain balance load voltages under varying loads, it is necessary to solidly connect the primary and secondary neutrals to ground. This may allow some secondary current to flow on the primary neutral and may also cause interference with parallel communication lines.
wye-wye-delta transformer
a three-phase transformer in which the primary and secondary coils are connected in wye. In order to overcome the problems with the wyewye connection, a set of tertiary coils are connected in delta to provide a path for the triple harmonic components of the exciting current to circulate.
X-ray
short wavelength electromagnetic radiation; often considered to range from about 0.1 to 100 °A.
X-ray lithography
lithography using light of a wavelength in the range of about 0.1 to 5 nm, with about 1 nm being the most common, usually taking the form of proximity printing.
Y connection
a three-phase source or load which is connected such that the elements are connected in parallel and are thus represented in a schematic diagram in a Y or star–shaped configuration.
Z
See impedance
Z<sub>L</sub>
common symbol for load impedance.
Z<sub>S</sub>
common symbol for source impedance.
Z-bus
matrix which contains the impedance of each element in an electric power system.
zero-sequence reactance
the reactive component of the zero sequence impedance.
See symmetrical component
zig-zag ground
(1) a grounding arrangement which is used to supply single phase grounded circuits from an ungrounded three-phase delta connected electric power line.

(2) the winding arrangement within a grounding transformer.
zinc oxide arrester
a lightning arrester that consists of a stack of ZnO disks stacked within a vented porcelain tube. See gapless arrester.
zone of protection
the area of a power system for which a particular set of protective relays has primary protection responsibility. In typical cases, operation of any of these relays will open circuit breakers which will isolate this zone. Each major power system component (line, transformer, bus, generator) has a separate zone of protection.
rectifier
a circuit that changes an AC voltage to DC. Switching elements or diodes are used to create the DC voltage. Diode rectifiers
and thyristor rectifiers are the two most commonly used rectifiers.