All Electric Control System
Mater Control Station (MCS)
An Example of a Well Status Display on MCS
Electrical Power Unit (EPU)
Hydraulic Power Unit (HPU)

The following subsea control system components should be located on the host facility (topside):

  • Master control station, including the human/machine interface;
  • Electrical power unit;
  • Hydraulic power unit;
  • Topside umbilical termination assembly.

Master Control Station (MCS)

The MCS is necessary for any electrohydraulic multiplexed subsea control system. It provides the interface between the operator and the subsea equipment. Because the system operates using electronic messages between the surface and subsea equipment (SCM, sensors, etc.), some form of communication subsystem is required in i t. The MCS interfaces with the topside equipment via a supervisory control network. Functions include executing safety shutdown, subsea well and manifold control, and data acquisition. The operator interfaces with the MCS through a human/machine interface (HMI), which comprises a keyboard and a visual display. A separate HMI may be provided for downhole sensors and their associated electronic equipment. The functions of an MCS usually include the following operating modes:

  • Tree valve control;
  • Choke control;
  • Subsea sensor monitoring/fast scan;
  • Interlocks;
  • Alarm announcements;
  • Workover;
  • Emergency shutdown;
  • Well test management;
  • Hydrate region warning;
  • Trends/historical data reporting and data logging. The MCS is typically made up of a number of units, including computers, displays, and controls.

Electrical Power Unit (EPU)

Any electrohydraulic multiplexed subsea control system requires a topside unit to control and provide the necessary power to the subsea equipment. The EPU supplies dual, isolated, single-phase power for the subsea system through the composite service umbilical, together with power supply modules for the MCS and HPU. The EPU supplies electrical power at the desired voltage and frequency to subsea users. Power transmission is performed via the electrical umbilical and the subsea electrical distribution system.

Hydraulic Power Unit (HPU)

The fluid is supplied via the umbilical to the subsea hydraulic distribution system, and to the subsea control module (SCM) to operate subsea valve actuators. The HPU supplies the necessary hydraulic fluid and comprises, among others:

  • Hydraulic pump aggregate;
  • Hydraulic tank;
  • Eventual pressure compensation system if the HPU is running submerged;
  • Main filters and system pressure valves.


1] Society for Underwater Technology, Subsea Production Control, SUT, Subsea Awareness Course, 2008.

[2] B. Laurent, P.S. Jean, L. Robert, First Application of the All-Electric Subsea Production System Implementation of a New Technology, OTC 18819, Offshore Technology Conference, Houston, 2006.

[3] C.P. William, Subsea Control Module, U.S. Patent 6,161,618, 2000.

[4] International Electro-technical Commission, Functional safety of electrical/electronic/ programmable electronic safety-related systems, IEC 61508, 2010.

[5] J. Davalath, H.B. Skeels, S. Corneliussen, Current State of the Art in the Design of Subsea HIPPS Systems, OTC 14183, Offshore Technology Conference, Houston, 2002.

[6] International Organization of Standards, Petroleum and natural gas industries - Design and operation of subsea production Systems - Part 6: Subsea production control systems, ISO 13628, 2000.