SECTION V GAS GATHERING STATION
5.1 ELECTRICAL SYSTEMS
5.1.2 Electrical System Start-Up
Condition-A – Plant Electrical System Start-Up Sequence
During initial start-up of the plant, the following sequence of operations shall be followed. Seven steps are described below:
Step 1: The objective is to start the EDG for plant start-up.
o Ensure that incomer breakers and outgoing feeders of the Plant Emergency MCC are all OPEN.
o Start manually, the Emergency Diesel Generator set from the Local Power Panel or EDG control panel of the EDG set.
(a) Black Start: The EDG set can be started if the starting batteries are in fully charged condition. The starting batteries of the EDG set are rated for 3-starts with an interval of 10-sec before lockout. Alternatively, the EDG can be started using compressed air system with sufficient storage to provide air for 3-starts with an interval of 10-sec.
(b) Energize the Emergency MCC by closing the DG Incomer Breaker on to the Dead- Bus. The closing of the breaker is automatic if DC-UPS power is available and is
carried out manually from the LV switchboard if the DC-UPS supply is not available.
Step 2: The objective is to energize all emergency and critical process loads connected to the GGS Substation for Plant start-up.
Following critical loads on the Emergency Switchboard are to be switched ‘ON’ manually or from MCCS.
o Outgoing feeders to Main Emergency Lighting Distribution Board connected to emergency switchboard
o Outgoing feeder to Auxiliary Distribution Board of EDG o Outgoing feeder to substation HVAC panel
o Outgoing feeder to control room HVAC panel o Outgoing feeder to substation AC UPS
o Outgoing feeder to substation DC UPS
Additionally any or all of the following loads can be switched ‘ON’, as required from the switch itself.
o Outgoing feeder to Emergency Auxiliary Distribution Board o All outgoing feeders from 230 V AC UPS Distribution boards o All outgoing feeders from 110 V DC UPS Distribution boards o Outgoing feeder to Switchboard for GTG-A or B
o Outgoing feeder to other critical loads, if any
Based on the process requirement, the following process loads fed from emergency MCC can be started from ICSS through the PMS, as the case maybe.
o
Outgoing feeder to Instrument Air Compressor-A/B/C (only one allowed to start)o Outgoing feeder to HP & LP Methanol Injection Pump Electric Motor o Outgoing feeder to nitrogen Generation Electric Heater Thyristor Control
Panel
o Outgoing feeder to Flare KO Drum Pump Electric Motors
o Outgoing feeder to Flare KO Drum Thyristor controlled Electric Heater. o Outgoing feeder to other critical process loads (if any) connected to the
Emergency Switchboard
Step 3: Objective is to start GTG and energize the 11 kV switchboard.
Energization of 11 kV switchgear at the Substation: The dead-bus closing of the bus-tie from common synchronising panel is to be carried out. PMS will generate hard-wired close
permissive interlock for closing circuit of incomer breaker after ensuring that 11 kV switchboard is healthy and all incoming and outgoing feeder breakers are open. (In manual mode 11 kV Incomer and Bus Tie Breakers can be closed in Test position from
switchboard). Operator to ensure that the 11 kV switchboard is a continuous bus with all bus-coupler breakers closed before closing the incomer breaker during plant start-up condition.
Identify and start one of the GTGs (either GTG-A, or GTG-B). The feeders of the GTG-Auxiliaries shall be in ready to start condition, so that they can start when the signals are received from the GTG-UCP. The list of GTG Auxiliaries is as follows:
o Starter Motor
o Lubricating Oil Pump Motor o Oil Mist Eliminator Fan o Liquid Fuel Oil Pump
o Main Enclosure Vent. Fan 1 & 2 o Vent Air Filter Fan Bleed Fan o Wash Water Skid Motor o ABLOC Fan 1, 2 & 3 o CACA Fan 1 & 2
o Lube Oil Tank Heater No-1, 2 & 3 o GT Gas Fuel Trace Heating o Fire Protection System o Engine Cleaning Unit o Combustion Air Filter
o Ventilation Air Intake Fan Motor Control
All these feeders are housed in the respective Gas Turbine Generator MCC Switchboard fed from the Emergency MCC.
The first GTG is brought into circuit by dead-bus closing of its 11 kV incomer breaker. The incomer circuit breaker ‘Close’ command from CSP is routed through PMS to ensure that 11 kV switch board is healthy and only one Neutral Earthing Resistor (NER) is in circuit for earthing of neutral of 11 kV system.
On closing of the first GTG incomer breaker on to the HV switchboard, the 11 kV system gets energized and the 11 kV bus Voltage, kW and current feedback along with breaker status is available to the PMS and selectively to ICSS.
Step 4: Objective is to energize the Distribution
On receipt of the above information, the Operator from PMS initiates the closing of the 11 kV distribution transformer breakers at the HV switchboard and charges the
Steps 5: Objective is to energize the Switchboards
o Close breakers 52-U1 & 52-U2, 52-P1 & 52-P2 (323-MMS-1-1) and energize the Utility and Process MCC Switchboard with the respective Bus-coupler breakers kept open.
Step 6: Objective is to switchover from the EDG supply to GTG power
o Close tie breaker -52E1 in the Utility MCC to supply LV power from the Utility MCC Switchboard to the Emergency Switchboard.
o Operator to initiate the Auto-synchronizing of the Tie Breaker-52E2 (These tag Nos. are with respect to operating philosophy SLD) (Refer Doc. 300-EEL- DBP-001) (Emergency Switchboard) either from the PMS or from the EDG GCP (EGCP) panel. The synchronizing of the EDG is done by the synchronizing panel within EGCP. On achieving synchronism (of EDG with normal supply) the command to close the Tie Breaker-52E2 is issued by the EDG GCP panel automatically.
o On closure of Breaker-52E2 in the Emergency Switchboard, the normal and EDG supplies are running in parallel and feeding the Emergency Switchboard load.
o This is followed by un-loading of the EDG and tripping the EDG incomer Breaker-52E2 from the EDG- GCP panel.
At this stage, all the main HV & LV switchboards (Utility, Process & Emergency) are energized and in normal operation. The HV & LV loads of Process and Utility can be started.
Step 7: Objective is to start the other GTG (if required) and HV loads with pre-conditions of the minimum power requirements.
With the normal and emergency LV loads in operation, the first GTG is fully loaded. Based on the process operating requirement, the operator has to decide on the starting of the other GTG. The standby HV motor loads are to be started considering the running reserve capacity of the GTGs.
Identify and start the second GTG (either GTG-A or GTG-B)). The feeders for the GTG-Auxiliaries are kept in ready to start condition, so that they can start when the signals are received from the GTG-UCP.
Once the voltage and frequency builds, start-up of second GTG is complete, operator to initiate the Auto-synchronizing of the Incomer breaker from the PMS. On achieving synchronism, the command to close the Incomer breaker-52E2 is issued by the GTG common synchronizing panel automatically.