20-07-2012, 04:27 PM
Basic Design Requirement - Electrical Equipment
41279291-Basic-Design-Requirement.pdf (Size: 101.46 KB / Downloads: 42)
Generators
a. The generator shall be designed, constructed and tested in accordance with IEC Publication No. 34 and other relevant parts dealing with rotating electrical machines.
b. The temperature of armature and field windings shall not exceed 130 oC when delivering rated MVA continuously at rated voltage, power factor and frequency, and with a temperature of canal water of 30 oC and with only 75% of the cooling system working. The temperature of the armature winding shall be determined in operation, by means of resistance type temperature detectors embedded in the windings. The ambient temperature shall be taken as 50 o
c. The generator and all accessories shall be capable of withstanding all temperature changes and sudden three phase short circuit, at its terminal without damage to any equipment.
Excitation and Voltage Regulation System
The recommended excitation and voltage regulating systems shall be modern static type. However, the final decision would be taken by the Employer in coordination with the Contractor as regards the static excitation or the rotary excitation types.
The voltage regulator shall have the following main functions:
• Voltage regulation
• Field current regulation
• Field current limiter
• Reactive compensation
• Supervision and logic circuits
• Following line voltage during synchronising
• Under excitation limiter
• Stator current limiter
• Power system stabilizer
• Power factor regulator
• Active compensation
Transformers
Two (2) main step-up transformers and two (2) auxiliary transformers shall be installed. The main transformers shall be coupled to the generating voltage of 6.3 kV and stepped up to 11 kV. The step-up transformers shall be installed in open air adjacent to the powerhouse and linked by cable to the 11 kV switchgear. The delta connected winding shall provide a closed circuit for third harmonics currents. The high voltage winding shall be Y connected with the neutral taken out on a separate terminal for connection to earth. Auxiliary transformers shall be installed for the power plant auxiliary supply system. Transformers installed outdoors shall be conventional oil immersed and hermetically sealed. Indoor transformers shall be dry – type.
The high and low voltage transformer bushings shall be sealed by suitably designed terminal cover boxes and cable sealing ends so as to prevent ingress of moisture, insets and other objects to prevent possible short circuits and accidents.
Low Voltage AC Supply (400 V)
The low voltage AC distribution system shall be designed as a 400 V, 3 phase four wire plus protective (earth) conductor system. Normally the station service
bus shall be supplied by the station transformer connected to the 11 kV bus. In emergency cases, a standby diesel generating set shall start automatically and provide power to supply essential station loads as well as start-up load of one unit. A third source of auxiliary supply shall be from 11/0.4 kV, 300 kVA auxiliary transformer fed from 11 kV line. This supply will also serve for initial testing of the plant, commissioning tests and for essential supplies during canal closure.