Electronics Guide

Drawworks and Top Drive Systems

The drawworks raises and lowers the drill string, requiring precise speed and torque control at power levels ranging from hundreds of kilowatts to several megawatts:

Modern drilling systems use variable frequency drives (VFDs) or DC drives with silicon-controlled rectifier (SCR) power conversion. These drives generate conducted emissions across a broad frequency spectrum, with significant harmonic content at multiples of the switching frequency. The high power levels involved can create interference affecting equipment throughout the platform if proper filtering and shielding are not implemented.

The drawworks control system must maintain accurate position and speed control despite electrical noise from its own drive and from adjacent equipment. Position feedback from encoders or resolvers travels through an electrically noisy environment where interference could cause measurement errors with safety implications. Fiber-optic feedback connections eliminate electromagnetic coupling concerns.

Top drives rotate the drill string during drilling operations. The electrical connection to the rotating top drive uses slip rings or twist cables that can generate electrical noise. The control signals must also be transmitted to the moving top drive without interference corruption.

Mud Pump Systems

Mud pumps circulate drilling fluid through the well at pressures up to 7,500 psi, using electric motors rated at 1-3 MW each:

VFD-controlled mud pumps allow precise control of flow rate but generate substantial electromagnetic emissions. Multiple mud pumps operating simultaneously create an aggregate interference level that must be considered in the EMC design.

Mud pump pressure and flow instrumentation is safety-critical because sudden changes can indicate well control problems. These instruments must provide accurate readings despite the electromagnetic noise from the pump motors and drives.

Measurement While Drilling (MWD) Systems

MWD systems transmit real-time data from downhole sensors to the surface, using either mud pulse telemetry or electromagnetic transmission through the earth:

Electromagnetic MWD systems inject low-frequency signals (typically 2-12 Hz) into the drill string for transmission through the earth to surface receivers. These systems are highly susceptible to electromagnetic interference from the drilling equipment, particularly from VFDs that generate harmonics in the same frequency range.

Surface receivers must extract weak telemetry signals from a background of interference from drilling equipment, platform electrical systems, and sometimes deliberate electromagnetic transmissions for well logging purposes. Signal processing techniques including digital filtering and correlation detection help recover signals from noise, but reducing interference at the source through proper EMC design remains essential.

Mud pulse telemetry systems are less susceptible to electromagnetic interference because they use pressure pulses rather than electrical signals for transmission. However, the surface pressure sensors and signal processing electronics can still be affected by EMI.

Drilling Instrumentation

The driller relies on numerous instruments to monitor and control drilling operations:

Weight on bit, rotary torque, and hook load measurements use strain gauge sensors that produce low-level analog signals susceptible to electromagnetic pickup. Signal conditioning electronics near the sensors and shielded transmission to the driller's console help maintain measurement accuracy.

Pit volume totalizers and flow meters monitor drilling fluid volume to detect kicks (influxes of formation fluid into the wellbore). These safety-critical measurements must be reliable despite interference from mud pump VFDs and other equipment.

The driller's console integrates displays and controls for all drilling functions. This console must be designed to meet EMC requirements appropriate for a control room environment and must maintain reliable data communication with sensors and actuators throughout the drilling area.

Distributed Control Systems

Modern offshore facilities use distributed control systems (DCS) with control rooms, remote I/O stations, and field instruments connected by data networks:

The control room houses operator workstations, engineering stations, and central processing equipment in a controlled environment. EMC considerations for the control room include proper grounding of equipment cabinets, separation of power and signal cables, and protection against electromagnetic fields from external sources.

Remote I/O stations located throughout the platform collect data from field instruments and distribute control signals to actuators. These stations are often in electrically noisy locations near large motors or switchgear. Proper cabinet design, cable entry treatment, and internal wiring practices are essential for reliable operation.

Field instruments including transmitters, analyzers, and valves must operate correctly in the platform's electromagnetic environment. Instruments certified for installation in hazardous areas undergo EMC testing as part of their certification, but proper installation is equally important for achieving reliable operation.

Field Networks and Communication

Process control communication uses various technologies including 4-20 mA analog, fieldbus protocols (Foundation Fieldbus, Profibus), and industrial Ethernet:

Traditional 4-20 mA analog signals are relatively robust against electromagnetic interference because the current signal is less affected by voltage noise than voltage-mode transmission. However, the signal cables can still pick up interference that appears as measurement noise or errors.

Digital fieldbus communication offers advantages including reduced wiring and self-diagnostics, but requires attention to cable installation and grounding to maintain reliable communication. Foundation Fieldbus H1 uses intrinsically safe signaling that can be installed in Zone 1 hazardous areas with proper design.

Industrial Ethernet provides high-speed communication for advanced control strategies and historian data collection. The higher data rates require more attention to cable quality and installation practices to maintain signal integrity in the presence of electromagnetic interference.

Variable Speed Drives in Process Systems

Pumps and compressors throughout the process system may use variable speed drives for efficiency and control flexibility:

While individual process drives are typically smaller than drilling equipment drives, a production platform may have dozens of VFDs with aggregate emissions that significantly affect the electromagnetic environment. A platform-wide approach to EMC design considers the cumulative effect of all drives.

Process compressor VFDs may include harmonic filters or active front ends to reduce their impact on power quality and conducted emissions. The additional cost of these features is often justified by the overall improvement in platform electromagnetic environment.

Subsea systems increasingly use variable speed drives for pumps and compressors located on the seabed. These drives must be designed for the unique challenges of subsea installation, including long power cable runs that affect both EMC and power quality.

Analyzer Systems

Process analyzers measure gas composition, water content, and other parameters critical for process optimization and custody transfer:

Gas chromatographs and other sophisticated analyzers contain sensitive electronics that can be affected by electromagnetic interference. These instruments are often located in analyzer shelters that provide some protection from the platform's electromagnetic environment.

Analyzer output signals transmitting measurement results to the control system must be protected from interference that could corrupt the readings. Proper shielding and grounding of signal cables is essential.

Custody transfer analyzers used for fiscal measurement are subject to particularly stringent accuracy requirements. Any EMC-related measurement errors could have significant financial implications.

Emergency Shutdown Systems

Emergency shutdown (ESD) systems detect hazardous conditions and take automatic action to bring the facility to a safe state:

ESD logic solvers must be immune to electromagnetic interference that could cause either spurious trips (unnecessary shutdowns) or failure to trip when required. Both failure modes have serious consequences: spurious trips cause production losses and may create their own hazards, while failure to trip can result in accidents.

ESD input circuits receive signals from safety sensors throughout the platform. These circuits must be designed to reject electromagnetic noise while responding correctly to genuine alarm signals. Input validation techniques including sensor redundancy help distinguish between interference and real process deviations.

ESD output circuits actuate shutdown valves, trip relays, and other final elements. The output signals must reach the final elements reliably despite the electromagnetic environment, even during upset conditions when electrical transients may be present.

ESD system power supplies must be protected against conducted interference and must continue operating through voltage dips and transients that might occur during emergency conditions.

Fire and Gas Detection

Fire and gas detection systems provide early warning of hazardous conditions:

Gas detectors sense the presence of flammable or toxic gases using various technologies including catalytic, infrared, and electrochemical sensors. These detectors must not generate false alarms from electromagnetic interference, yet must reliably detect actual gas releases. False alarms are particularly problematic because they can lead to alarm fatigue where operators dismiss genuine warnings.

Fire detection uses heat detectors, smoke detectors, and flame detectors distributed throughout the platform. Each technology has specific EMC characteristics. Flame detectors using UV or IR sensors can be affected by interference from welding operations or other sources of UV/IR radiation.

The fire and gas control panel processes detector signals and initiates appropriate responses. Like the ESD system, this panel must be immune to interference that could cause inappropriate response or failure to respond.

Detector communication may use addressable loops, radio links, or hardwired connections. Each approach has different EMC considerations. Addressable loops carry digital communication that must be protected from interference, while hardwired systems rely on analog signal integrity.

Process Safety Time Critical Functions

Some safety functions must respond within specific time limits to prevent hazardous situations from developing:

High-integrity pressure protection systems (HIPPS) must close isolation valves before pressure can rise to dangerous levels. The response time requirement leaves no margin for interference-induced delays in signal processing or actuation.

Blowdown systems rapidly depressurize equipment to prevent catastrophic failure during fire conditions. The system must initiate correctly in response to confirmed fire detection while resisting spurious activation from electromagnetic interference.

Safety systems addressing time-critical functions typically use dedicated instrumentation with the shortest practical signal paths and minimal opportunities for interference to affect system response.

Safety System Testing

Regular testing verifies that safety systems will function when required:

Proof testing procedures should include verification that safety functions operate correctly in the actual electromagnetic environment, not just in laboratory conditions. A safety system that passes bench testing may fail in service if installation-specific EMC issues were not addressed.

Partial stroke testing of safety valves verifies valve operation without fully closing the valve. The electronic controllers performing partial stroke tests must be immune to interference that could cause incorrect test results or inadvertent valve closure.

Helideck Communication Systems

VHF air band radio communication between the helicopter and platform must be free from interference:

The helideck radio operates in the 118-137 MHz aviation band. Platform radio systems, particularly VHF marine radio in the adjacent 156-162 MHz band, must not generate spurious emissions that could interfere with aviation communications.

During critical phases of flight including approach and landing, any communication interference could compromise safety. The platform's radio frequency environment should be assessed to ensure adequate margin against interference.

Navigation Aid Protection

Helicopter navigation systems must function correctly near the platform:

GPS receivers on helicopters are susceptible to interference from platform radar and communication systems. The field strengths near the helideck from these sources should be calculated and measured to verify they remain below levels that could affect helicopter GPS.

Radio altimeters operating at 4.2-4.4 GHz can be affected by interference from platform equipment. This frequency range should be protected from spurious emissions.

Some platforms have instrument approach systems that must be protected from electromagnetic interference that could affect their accuracy.

Helideck Lighting

Helideck lighting systems must be visible and reliable without causing electromagnetic interference:

LED helideck lights have replaced incandescent lights on many platforms, offering improved reliability and lower power consumption. The LED drivers must be designed to minimize electromagnetic emissions that could affect aviation or platform radio systems.

Obstruction lighting on the platform structure uses high-intensity lights visible from aircraft. These lights and their controllers must not generate interference with helicopter systems.

Helicopter Refueling

Helicopter refueling creates potential ignition hazards that require attention to both electrical bonding and EMC:

During refueling, the helicopter must be electrically bonded to the platform to prevent static discharge that could ignite fuel vapors. This bonding must provide a low-impedance connection while not creating ground loops that could affect electronic systems.

Radio transmissions may be restricted during refueling to prevent RF-induced currents from creating ignition sources. The platform's radio frequency environment assessment should identify any restrictions required.

Satellite Communication

Satellite links provide voice, data, and video communication with onshore facilities:

VSAT (Very Small Aperture Terminal) systems operating at C-band, Ku-band, or Ka-band provide high-bandwidth communication for real-time data transmission and video conferencing. The satellite terminal must be located where it has clear line of sight to the satellite while being protected from interference by platform radar and radio systems.

The satellite uplink transmitter can potentially interfere with other platform systems if spurious emissions are not adequately controlled. Careful frequency coordination and proper equipment specification help prevent interference.

Backup satellite communication systems using different frequency bands or satellite networks provide communication resilience for emergency situations.

Radio Systems

Platforms use various radio systems for different purposes:

Marine VHF radio provides ship-to-shore and ship-to-ship communication and is required for GMDSS compliance. The VHF installation must follow maritime EMC requirements.

UHF or VHF hand-portable radios provide on-platform communication for operations and safety. These radios operate throughout the platform, including in areas with high electromagnetic field levels from industrial equipment. Both the immunity of the radios to interference and their potential to cause interference must be considered.

In hazardous areas, radio equipment must be certified for use in explosive atmospheres. Intrinsically safe radios limit energy levels to prevent ignition while maintaining communication capability.

Telemetry and SCADA

Platforms communicate with shore-based control centers and with other offshore facilities:

SCADA (Supervisory Control and Data Acquisition) systems transmit operational data to onshore control rooms and receive control commands. The communication links, whether satellite, microwave, or subsea fiber, must provide reliable data transmission despite the platform's electromagnetic environment.

Subsea control systems communicate with wells and subsea equipment through umbilicals that may be many kilometers long. These communication links use various technologies including electrical signals, fiber optics, and hydraulic signals, each with different EMC characteristics.

Crew Welfare Communications

Modern platforms provide communication facilities for crew welfare:

Telephone and internet services for crew personal use often share infrastructure with operational communications. The aggregate electromagnetic emissions from crew devices (mobile phones, laptops, tablets) can affect the platform's electromagnetic environment.

WiFi networks for crew access should be designed to avoid interference with platform control systems and to meet any restrictions on radio emissions in hazardous areas.

Power Generation

Most offshore platforms generate power using gas turbines or diesel engines driving generators:

Generator voltage regulators and excitation systems use power electronics that can generate harmonics and transients. Modern digital AVRs (automatic voltage regulators) require EMC-conscious design to prevent interference from affecting voltage regulation accuracy.

Multiple generators operating in parallel require synchronization and load sharing controls. The sensing and control electronics for these functions must be immune to the electrical noise present on the platform power system.

Some platforms receive power from shore through subsea cables. These long cables can affect power quality and create unique EMC considerations at the cable terminations.

Medium Voltage Distribution

Larger platforms distribute power at medium voltage (typically 6.6 kV or 11 kV) to reduce cable sizes and losses:

MV switchgear generates significant electromagnetic fields during switching operations. The transients produced by vacuum or SF6 circuit breakers have very fast rise times with frequency content extending into the megahertz range.

Protection relays and metering equipment in MV switchgear must operate correctly despite the electromagnetic environment. Modern numerical relays include EMC certification as part of their type approval.

Medium voltage VFDs for large motors generate substantial electromagnetic emissions that require proper filtering and shielding. The long cable runs sometimes required between MV drives and motors can act as effective antennas for radiated emissions.

Low Voltage Distribution

Most platform equipment operates at low voltage (typically 400/230 V or 480/277 V):

LV distribution panels throughout the platform provide power to local equipment. These panels should be designed with EMC in mind, separating power and control sections and using appropriate cable entry treatment.

Uninterruptible power supplies (UPS) for critical loads generate conducted emissions from their inverter sections. The UPS output filtering must be adequate to prevent interference with connected equipment.

Emergency generators and their associated distribution provide backup power during main power failures. These systems must function correctly under abnormal conditions when the electromagnetic environment may be disturbed.

Earthing and Bonding

A comprehensive earthing system is essential for both safety and EMC:

Platform structural steel provides a low-impedance earth reference. All equipment frames and enclosures should be bonded to the structure with connections that maintain low impedance at high frequencies.

Instrument and control system earthing requires particular attention to prevent ground loops while providing effective EMC protection. Various earthing philosophies are used including isolated earth reference, mesh earth, and hybrid approaches.

Cable shield earthing practices affect EMC performance. Shields may be earthed at one end, both ends, or both ends with a continuous connection to earth along the cable route, depending on the cable type and installation conditions.

HVAC Systems

Climate control for accommodation uses multiple fan coil units and air handling systems:

Variable speed drives for HVAC fans can generate interference affecting cabin entertainment systems and personal electronics. Proper filtering and installation practices keep interference levels acceptable.

HVAC control systems using building management protocols must communicate reliably despite interference from fan drives and other electrical equipment.

Entertainment and Communication

Crew welfare facilities include television systems, internet access, and telephone services:

Television distribution systems using coaxial cable can both emit and receive interference. Proper shielding and grounding maintain signal quality and prevent emissions.

WiFi and cellular services in accommodation areas must not interfere with platform operations and must meet any restrictions applicable in hazardous areas adjacent to accommodation.

Emergency Systems in Accommodation

Emergency lighting, fire detection, and public address systems in accommodation must function reliably:

These systems use the same technologies as those in process areas but may have different installation requirements due to the accommodation environment. EMC performance should be verified for the specific installation.

Hazardous Area Classification

Areas are classified according to the likelihood of explosive atmosphere presence:

Zone 0: Explosive atmosphere present continuously or for long periods (rare on platforms)

Zone 1: Explosive atmosphere likely during normal operation

Zone 2: Explosive atmosphere not likely during normal operation but may occur for short periods

Equipment installed in hazardous areas must be certified for the zone in which it is installed. This certification includes EMC testing to ensure the equipment does not generate electromagnetic fields that could cause ignition.

Intrinsically Safe Equipment

Intrinsic safety limits electrical energy to levels too low to cause ignition:

Intrinsically safe circuits must maintain energy limits under both normal operation and specified fault conditions. EMC protection devices must be selected to maintain intrinsic safety while providing adequate EMC performance.

The interconnection between intrinsically safe field devices and non-intrinsically safe control equipment requires isolating barriers or galvanic isolation that can affect EMC characteristics of the circuit.

Ground connections in intrinsically safe systems are carefully controlled to prevent earth faults that could compromise safety. These grounding requirements must be coordinated with EMC grounding practices.

Radio Frequency Considerations

Radio frequency energy can cause ignition in hazardous areas:

High-power RF transmitters can induce currents in metallic structures that create sparks. The RF environment must be assessed to ensure that induced currents remain below ignition thresholds.

Hand-portable radios used in hazardous areas must be certified for hazardous area use. The certification considers both the radio's own emissions and its potential to induce currents in nearby structures.

Radar and satellite communication transmitters are typically located outside hazardous areas, but their emissions must be considered in the hazardous area assessment.

Static Electricity

Static discharge can ignite explosive atmospheres:

All conductive items in hazardous areas must be bonded and earthed to prevent static charge accumulation. This bonding must not create paths for interference currents that could affect electronic systems.

Non-conductive items can accumulate static charges that cannot be dissipated through bonding. Antistatic materials and humidity control help manage static in these situations.

Personnel entering hazardous areas may carry static charges. Earthing provisions at zone boundaries allow personnel to discharge before entering.

Equipment Selection

Equipment should be specified to meet appropriate EMC standards:

For equipment in process control applications, the relevant standards include IEC 61326 (EMC for industrial process measurement and control) and IEC 61000-6-2/6-4 (generic industrial immunity and emission standards).

Marine-type approved equipment meeting IEC 60945 may be appropriate for some applications, particularly communication and navigation equipment.

Equipment for hazardous areas must be certified for the specific zone classification, with the certification including EMC testing appropriate for the application.

System Design

EMC considerations should be integrated into the system design:

Cable routing plans should identify segregation requirements for different cable categories based on their EMC characteristics. Power cables, VFD motor cables, and sensitive signal cables should be routed separately.

Earthing and bonding system design should address both safety and EMC requirements, with clear documentation of the intended earthing philosophy and practices.

Equipment layout should consider electromagnetic compatibility, locating sensitive equipment away from known interference sources where possible.

Installation Quality

Installation quality has a major impact on EMC performance:

Cable installation must follow the specified segregation requirements. Cable trays should be properly earthed, and cables should be secured to prevent movement that could compromise shielding or create rubbing damage.

Cable shield terminations must be executed correctly, typically using 360-degree termination at connectors or gland plates rather than pigtail connections.

Equipment cabinet installation should ensure proper earthing of cabinet enclosures and correct installation of any specified EMC filters or ferrites.

Commissioning Verification

EMC performance should be verified during commissioning:

System testing should include operation under realistic electromagnetic conditions, with interference sources operating as they would during normal platform operations.

Any EMC problems discovered during commissioning should be resolved before the platform enters operation. Temporary solutions may be acceptable for initial operations but should be replaced with permanent fixes at the earliest opportunity.

Documentation of the commissioning results provides a baseline for comparison if EMC problems develop later during the platform's operating life.