Variable Speed Drive (VSD)
The variable speed drive (VSD) is intended to manage, protect, control parameters and regulate rotation frequency of the electrical centrifugal submersible pump (ESP) with a submersible motor (ESM) with capacity of up to 400 kW VSD ensures ESM operation supplied by AC three-phase circuit.
VSD power supply is performed from AC electrical mains with the nominal voltage of 480 V, frequency of (50±1) Hz. Allowable range of voltage changes in electrical mains is from 340 to 550 V.
VSD secures ESM start-up, shutdown and control in compliance with the user’s setpoints.
Variable speed drive manages frequency regulation of rotor rotation of a submersible electrical motor:
- from 3.5 to 70 Hz with a discretion of 0.1 Hz for induction submersible electrical motors;
- from 15 to 240 Hz (to 6,000 rpm) with a discretion of 0.1 Hz from AC submersible electrical motors.
VSD controls effective values of linear voltages in the range from 0 to 600 V with a relative error no more than 2 %.
VSD controls ESM operational current value. The control is performed based on the primary winding of a three-phase oil transformer (in intermediate frequency operation mode - at the outlet from an intermediate frequency transformer) and recalculated by software into an ESM operational current value considering the transformer ratio of the three-phase oil transformer. The current is controlled with a relative error no more than 2 % in the range from 0.1 of VSD nominal current to the nominal current.
VSD controls insulation resistance of «three-phase oil transformer - cable - ESM» system in the range from 1 to 10 Mohm with relative error no more than 10 % and in the range from 0 to 1 Mohm with relative error no more than 2.5%. VSD receives information from external equipment (submersible telemetry), via interface output RS485 or RS232.
VSD protects ESP from emergency operation modes resulting from the following failures in electrical circuit:
- voltage decrease below the low voltage setpoint;
- voltage increase higher than the high voltage setpoint;
- voltage unbalance in phases;
- violation of phase sequence;
- phase loss.
VSD additionally performs the following functionality:
- smooth motor acceleration and deceleration at a pace controlled by the setpoint;
- reverse motor rotation;
- ramp-up mode with the reverse to ensure ESP unseizure by sending overvoltage impulses to motor together with periodical reversed rotation;
- inching mode to start-up electrical submersible pump in case of motor heavy start by supplying overvoltage impulses to motor without reversed rotation;
- ESP shake mode, whereby operational frequency changes abruptly (decreases) down to the set frequency in a given period of time with further acceleration at a given pace to prevent deposits on stages of the submersible pump;
- gas pumping mode to ensure pumps operational availability in case of gas locking by increasing motor rotation frequency;
- building up sinusoidal voltage at the VSD output (in case of induction motor operation mode) by means of an integrated high order harmonic sine filter; voltage waveform distortion factor at VSD outlet does not exceed 5 %.