Читать книгу Practical Power Plant Engineering - Zark Bedalov - Страница 65

The 4.16 kV connected load is estimated to be around 15 MW at 0.8 pf (18.7 MVA). The 4.16 kV loads are critical loads for the plant production, requiring adequate availability of power supply. To establish the highest level of availability of the plant, the MV load board will be supplied from two 13.8 kV feeders from the main substation. The MV (5 kV) control assembly will be used to feed the plant MV motors rated over 200–2000 kW and 2/3 MVA, 4.16 kV to 480 V unit substations (Figure 2.9). The 4.16 kV loads will be controlled by the MV controllers, employing MV‐fused 400 A contactors.

The MV motor control assembly will be located close to the plant. It will have two incoming 4.16 kV switchgear feeder cells and a tie breaker. Each incomer breaker will be rated 2500 A to be able to carry the full MV load from a single incoming transformer of 12/15 MVA transformers.

The 4.16 kV motor control board is a metal enclosed assembly, NEMA class E2 (fused) with integral 120 V_ac control transformers. The four motor controller cells on each side will be attached to the regular 4.16 kV metal‐clad switchgear in the middle. The incoming breakers will automatically interact with the tie breaker on a 2 out of 3 switching principle to carry the full load in case of a transformer outage.

Nominal voltage	4.16 kV, 60 Hz, 3 ph, 3 w
BIL	60 kV
Switchgear, interrupting capacity	40 kA r.m.s. symmetrical
MV controllers, interrupting	40 kA r.m.s. symmetrical
Assembly	Metal‐clad/metal enclosed
Incoming and tie breakers	2500 A, vacuum type
Motor controllers (contactors)	400 A, fused, for up to 2000 kW maximum, NEMA E2

Figure 2.9 4.16 kV motor controller assembly.

The incomers and tie breakers are assembled in their metal‐clad, single cell enclosures. Motor and feeder controllers can be stacked up as two units per vertical section. The controllers for feeding the unit substation feeders are of latched type to ensure they are immediately energized and restored following a restoration from a power failure. The unit substation radial overhead feeders are protected by GE Multilin feeder protective relays, or equal, capable of automatic one shot reclosing. Each motor controller includes a set of medium voltage fuses, a vacuum contactor, and GE Multilin motor protector relay or equal. Fuses for the motors are of R‐rated type.

Fuses for the transformer and outgoing feeders are of current limiting L‐rated type (see Chapter 3).

All the breakers and controllers are provided with means of operating from local and remote positions. The means of communication for the breaker operation, interlocks, and status are by Ethernet from the control room (see Chapter 17).