Oil and gas production handbook An introduction to oil and gas production

Figure 36. Electrical single line diagram 

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118 
 
 
Voltage levels for high, medium and low voltage distribution boards are 13- 
130 kV, 2-8 kV and 300-600 V respectively. Power is generated and 
exchanged with mains or other facilities on the HV distribution board. Relays 
are used for protection functions.  
 
HV is transformed to MV switchboards, to which large consumers are 
connected. LV switchboards feed a mix of normal consumers, motor control 
centers (MCC) and variable speed drives for motors up to a few hundred KW 
(not necessarily separately, as shown in the figure below).  
 
A separate emergency power switchboard provides power for critical 
equipment. It can be powered from a local emergency generator if main 
power is lost. Computer systems are fed from an uninterruptible power 
system (UPS) with batteries, connected to the main or emergency 
switchboard. 
 
A power management system is used for control of electrical switchgear and 
equipment. Its function is to optimize electricity generation and usage and to 
prevent major disturbances and plant outages (blackouts). The power 
management system includes HV, MV and LV low voltage switchgear plus 
MCCs and emergency generator sets. Functions include prioritization of 
loads, emergency load shedding (closing down of nonessential equipment) 
and prestart of generator sets (e.g., when additional power to start a big 
crude pump is required). 
 
Large rotating equipment 
and generators are driven by 
gas turbines or large drives. 
Gas turbines for oil and gas 
production are generally 
modified aviation turbines in 
the 10-25 MW range. These 
require quite extensive 
maintenance and have a 
relatively low overall 
efficiency (20-27%, 
depending on application). 
Also, while a turbine is 
relatively small and light, it 
will usually require large and heavy support equipment such as large gears, 
air coolers/filters, exhaust units, and sound damping and lubrication units. 
 

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Therefore use of large variable speed drives is becoming more common. For 
pumps on subsea facilities, this is the only option. For use on remote 
facilities, High voltage DC transmission and HV motors can be used, from a 
main facility or power from shore. This avoids local power generation at each 
facility and contributes to low manning or remote operation. 
8.4  Flare and atmospheric ventilation 
Flare subsystems include flare, atmospheric ventilation and blowdown. The 
purpose of the flare and vent systems is to provide safe discharge and 
disposal of gases and liquids resulting from:  
 
•  Spill-off flaring from the product stabilization system. (oil, 
condensate, etc.) 
• Production 
testing 
•  Relief of excess pressure caused by process upset conditions and 
thermal expansion 
•  Depressurization, either in response to an emergency situation or as