SCR Power Control Systems

Total Rig Audit

Zeefax has developed a program to mitigate against unscheduled stoppages and breakdowns. It is a complete and holistic approach which aims to avoid stoppages but if they do occur, ensure that the resources are on hand to minimise the damage caused. This is the Total Rig Audit (TRA) by Zeefax and is carried out by our very specialised and highly experienced Field Service Engineers.

The Zeefax Total Rig Audit avoids downtime and ensures rig systems remain operational and reliable. Many Drilling Companies will invest in a completeRig Audit in the knowledge that it offers a comprehensive overview of the state of their rig, which can also be submitted for compliance and due diligence purposes.

Please contact us to book or inquire about Total Rig Audit

SCR Training Simulator

Every Drilling Rig must have a Power Control Room – sometimes also known as an SCR (standing for Silicon Controlled Rectifier) System – which forms the functional heart of the power control of the drilling operations. Typically, SCR systems comprise a large steel room, inside of which will be a range of Motor Control Centres, Engine & Generator Controls, SCR Control cubicles, and other instruments and systems used for drilling purposes.

SCR Systems usually operate at 600V, and clearly, these systems can be extremely dangerous if not operated correctly and carefully by suitably trained operators. It is therefore vital that drilling engineers and operators are well trained using a combination of class room tuition and on-the-job training.

In response to this need, Zeefax have created the world’s first full size SCR Training Simulator, which accurately mimics the a real SCR; it looks and feels like the real thing, providing a realistic experience of live field operations – but without the dangerous high voltage. This system was created specifically for Naftogaz – for more details, click here.

A key feature of the simulator is the addition of the on-board computer system, which mimics all of the signals that would normally come into this SCR system from the live engines and generators, including the motors running the mud pumps, the rotary table or the Drawworks, etc. and can also simulate a wide range of known faults, allowing trainees to experience first hand problem solving in the safety of the simulator, before they experience the live system.

Learn more about this full size training simulator – click here

GE Legacy Drive Systems

GE Oil Field SCR Systems 

Generation III

1970-1980’s….1800amp SCR Bays. They used a newer Woodward/Basler Generator control, as well as a different SCR Drive Control System. 

Micro Drill 1500

Used the same type SCR bridge as the Generation III, but rated at only 1200-1500 amp since the heat sink assembly is of a slightly different design. This system uses the GE generator GEM modules controls. 

Micro Drill 3000

1980’s, 900amp. SCR bridges using the GE GEM Generator Control. As the bridges are small it requires two SCR bays to run a two-motor Mud Pump or Drawworks. 

EGR (Engine Generator Regulator)

The newer GE generator controls out in the 1990’s is the EGR control. It is a direct replacement for the GEM module – see EGR page.

Engine Generator Regulator (EGR) Module

This module features digital circuitry providing enhanced control accuracy for speed and voltage, and also provides tools for system diagnostics, including “first fault” and multiple fault storage and annunciation. A fully featured internal diagnostic self-test on power up is provided, and available outputs include system KVA and kW limit protection.

The EGR is a direct replacement for the GEM Module and protects the engine through tachometer loss sensing, over speed detection, and reverse power protection with adjust-able time delay.

Test and Calibration Engineer – IMP products

Summary of the role

  • The repair, test and calibration of customer returned and new build data acquisition products and PCBs.
  • The work includes the use of small tools, soldering, use of circuit drawings and test specifications, and the completion of necessary paper work.
  • On the job training will be provided.

Specific job responsibilities

  • Manage and plan workload to ensure all jobs are achieved in a timely manner
  • Test and fault find on electronic products
  • Repair to component level on digital and analogue circuits on both through hole and SMT PCB’s
  • Calibrate and complete documentation and write accurate and concise test reports
  • Strip down and reassemble electronic products
  • Assess if a product is economical to repair and quote realistic repair time

Required qualifications and experience

  • Suitable electronics related qualification
  • Previous experience of electronic fault finding and repairing
  • Electronics manufacturing and or electronics service background, ideally in data acquisition
  • Must be able to follow circuit diagrams, assembly drawings and test specifications
  • Use a varied range of fault finding and test equipment
  • Soldering to a high quality standard on both through hole and SMT technology
  • Able to use own initiative and work with minimal supervision
  • PC literate with knowledge of Microsoft office packages, particularly Excel and Word

Additional information

  • There will be the possibility to work on customer’s site in the UK – including Nuclear Power Stations, who have installations which require periodic calibrations
  • This role may also include the possibility of occasional overseas travel.
  • For electronically creative technicians, there is also the possibility to work alongside our design engineers.

If you are interested in applying for this position, then please send us your latest CV and a covering letter to

Test and Calibration Engineer – SCR products


  • Will have studied electronics or electrical engineering to the equivalent of HND or degree level


  • At least 5 years working with printed circuit boards including testing, modification and repair at board level.
  • Working with micro controllers.
  • Working unsupervised on boards and control modules in the workshop and away from base.
  • Cubicle wiring including testing, correcting faults and commissioning.


  • Analogue and discrete digital circuits including thyristor control systems.
  • Low frequency op-amp standard circuits and the ability to analyse complex circuits and devise suitable tests.
  • Specification of circuit board components for a particular application.
  • Safety procedures for working with dangerous voltages in a test environment.


  • The use of hand tools including simple metalwork.
  • The use of personal computers including the creation of electronic and simple mechanical drawings.
  • The preparation of documents, reports and parts lists.
  • Sourcing components

If you are interested in applying for this position, then please send us your latest CV and a covering letter to

GE Micro Drill

GE Drive Services from Zeefax

Zeefax is the value source for parts and services for your legacy GE Drive and Generator Control Systems. We hold an inventory of critical spare parts and can provide comprehensive service solutions including Repair and Return of Modules and PCBs.

Repair and Return

Zeefax operates a comprehensive repair and return service for all legacy GE Drive and Generator Control Systems. which includes cleaning, testing, repairing or replacement of defective components and a full system load test. This service includes a 6-month limited warranty.

Re-manufacturing Services

Zeefax understands that replacement of a complete SCR Control System is often not viable due to the large cost and loss of production due to system downtime. At Zeefax we can offer a comprehensive service to support your legacy GE Drives and give it a renewed lease of life. That not only includes supply of spare parts and a repair/calibration service; qualified service engineers with years of experience with these Drives are available for regular Health Checks, fault-finding and general support purposes.



Zeefax Limited has been made aware that unauthorised individuals have masqueraded as Zeefax Limited, promising job opportunities in our name and requesting payments to cover processing fees, visas, work permits or other formalities. The job offers are typically supported by forged documents, giving the appearance of an official communication, including the use of the Zeefax Limited logo and links to the Zeefax Limited website.

Zeefax Limited (nor any of the placement firms that recruit on our behalf) will NEVER require potential candidates to make any form of advance payment as part of the hiring process.

These communications are fraudulent (usually from or and do not originate from Zeefax Limited (, nor are they associated with the Zeefax Limited recruiting process. The individuals who are sending these communications are doing so in an attempt to solicit money from potential job seekers. Be cautious of any unsolicited offers of employment particularly if you are requested to supply personal banking information or provide any form of advance payment.

If you suspect fraud, we would urge you NOT to respond to these unsolicited offers of employment, and to report such activity to your local law enforcement agency immediately!

Should you have any concerns over the validity of any correspondence received in respect of employment with Zeefax Limited, contact us directly at and we will investigate further.

PLC Programming

We have expertise in many of the commonly used devices, including Siemens, Allen-Bradley, GE Fanuc and Mitsubishi, and we have the operational experience and knowledge to provide completely new applications or modify existing ones. We are also able to help and advise on strategy and implementation, as well as with start-up and commissioning.


Zeefax PLC Training

Not only can we provide a comprehensive programming resource to help with your programming needs, we also can provide a series of PLC programming training courses. The comprehensive training experience is intended for those who wish to expand their skills and knowledge of PLC programming, fault finding and maintenance, and include modules for both novice and advanced users.

Course materials include information and techniques for a range of manufacturers including SiemensAllen-Bradley, GE Fanuc and Mitsubishi, and the curriculum may be tailored for specific requirements and needs, but will typically focus on the more practical aspects of Programmable Logic Controller applications.

All of Zeefax’s training courses are held in our design and manufacturing facility, located near London, England. To find out more about our training courses, please click here

Digital AutoSync Module

In response to many customer requests, we have designed our own version of the legacy Ross Hill Controls AutoSync AC generator control module; the new module has been completely re-designed and incorporates all new digital circuitry as well as optional expansion capability to future proof the module.

The new Digital AutoSync is not available from any other supplier in the world.

The use of modern digital circuitry and components has resulted in much improved parameter control over the previous legacy module without compromising operational reliability, and the ultra-stable frequency control system ensures safe and accurate control of generation systems.

The new front panel includes the familiar controls, but has been enhanced with the inclusion of an LCD display for module set-up and parameter display purposes; front panel controls include the manual circuit breaker and engine controls, with the addition of digital menu navigation buttons for module set-up and display options.


  • Completely redesigned and modernized
    • All new digital AC / AutoSync motor control module
  • Fully compatible with the now obsolete AC III module from Hill Graham Controls (HGC)
    • Can be retro-fitted directly with minimum changes to the existing control system
  • New Metering Functions
  • Hands-off-Cranking (H.O.C.)


The AC Regulator module associated with each generator section typically has four basic main functions:-

  • The exciter function
    • This controls the voltage and KVAR of the generator
  • The governor control function
    • This controls the speed and kilowatt output of the engine
  • The protection circuits for the engine and generator
  • The control and indicator function


Digital Control Modules

An important feature of the new modules is that they have exactly the same footprint and connection geometry as the old style legacy modules, making installation and upgrading of the new modules simple and quick.


Wire loom connections and attachment points are identical, meaning that no extra wiring or hardware is required in order to facilitate installation, and the new digital circuitry uses the latest available components and techniques, yielding enhanced reliability and performance over older legacy modules.

Our Research & Development department is currently working on new versions of the traditional AC and DC modules which will be available soon to add to the already released DDC and the Digital AutoSync.


These new modules will provide existing system users with a quick and cost effective upgrade path, maintaining the continuity and availability of well established installations.

To find out more about each of these new modules, click the corresponding menu items.

GE752 Motor Refurbishment

Zeefax is an established global supplier of high-quality and reliable electrical and mechanical engineering services. As part of the complete service we provide to the industry, we carry out repair and maintenance of all GE752 Motors, including:

  • Armature re-winds and replacement
  • Field re-winds and replacement
  • Connection box refurbishment
  • Replace supervisory sensors
  • Bearing replacement
  • Commutator refurbishment
  • Clean and Paint


Thyristors, Diodes and Fuses

Advancements in technology mean that many of the power semiconductors which were built into SCR systems 30 or more years ago have been superseded by new devices, often with improved specifications.

In order to take full advantage of available new technology, Zeefax can provide advice and sourcing for the latest systems and components.

Our engineers are able to ensure that, when the original component is not available, a suitable replacement can be found. If the replacement is not an exact fit, we can engineer an adaptation to ensure continued serviceability of legacy equipment.

Hill Graham Controls (HGC)

Zeefax Limited has been servicing the Drilling, Power Generation, Marine, Dredging and Oil & Gas industries Worldwide for almost four decades.

Following our acquisition of Hill Graham Controls (HGC), Zeefax is in a unique position to offer total support for all legacy Hill Graham and Ross Hill Controls (RHC) systems both in the UK and throughout the world.

Zeefax’s unique experience and expertise has allowed the company to design, manufacture, supply, repair and calibrate many of the control modules used within older Hill Graham installations, as well as other manufacturer’s systems, including Ross Hill Controls (RHC) type systems.

As well as the standard analogue AC and DC control modules, we are able to provide a complete service of maintenance and support including:

  • Supply of all printed circuit boards (PCBs), components and spare parts
  • Supply and Repair of all AC and DC Control Modules
  • Supply and Repair of all Marine DC Modules
  • Manufacture and Supply of new digital AC AutoSync Modules
  • Manufacture and Supply of new digital DDC Modules
  • Repair and Service of Hill Graham DDC, DFC, VFD, AF and FR modules
  • Engineered solutions to complex drilling issues

In recent times, Zeefax has developed and brought to market a new digital AutoSync module, with an improved contemporary design and operation. This advanced module occupies the exact same footprint and has pin-for-pin connection compatibility with the now obsolete Ross Hill module, thereby providing a simple and cost effective upgrade path for existing users of the AutoSync module.

These services mean that equipment manufactured up to 30 years ago, is still fully supported by Zeefax, and can continue to provide return on investment far beyond the normal life expectancy.

Troubleshooting & Maintenance

Zeefax has the experience to assist and provide engineers to troubleshoot issues, help during downtime, and establish a program of scheduled maintenance, targeted and customised for your individual requirements.

As part of our maintenance and service offerings for SCR systems, Zeefax is able to mobilise support and engineers to provide technical assistance during emergency shutdowns and downtime periods.

It is well established that a program of planned maintenance and support can and will ease pressure on people and systems, and can result in increased reliability, uptime and ultimately profitability of the system.

By predicting issues, and by scheduling maintenance, spare parts and manpower can be correctly scheduled, minimising downtime, keeping spare part inventory under control and avoiding unwanted breakdowns.

If you would like to know more about this, please call or email us, and we will be pleased to assist.

Installation & Commissioning

At Zeefax, we recognise that high-quality and experienced technical resources are required during major works, such as emergency breakdown repairs or un-scheduled downtime.

Given our years of experience and unique position to offer total support for all legacy Hill Graham Controls (HGC), and other manufacturer’s systems including Ross Hill Controls (RHC), IPS, and GE Micro Drill SCR systems, Zeefax can provide a full range of technical services for installation, commissioning, and ongoing operational support.

SCR System Health Checks

The time to find out if your system is reliable is when operations are quiet – not during critical well operations – so the Zeefax SCR System Health Check is designed to identify potential weaknesses and either repair or replace immediately, or mitigate against these until a repair or replacement can be effected – usually at a quite time.

Zeefax can help you to perform a comprehensive health check, and propose a detailed scope of work designed to compliment and conform to your operation schedule; this means that any potential disruption is absolutely minimised.

Special Requirements

Zeefax understands that each rig or vessel has different circumstances and different requirements. Our engineers are able to tailor a maintenance schedule to suit any installation or operational constraints. Where special equipment is required, such as secondary injection test equipment for testing circuit breakers, Zeefax will arrange to have the equipment on site, and our technician will be competent in its use.

Expert SCR Bridge Health Check

For reliable operation, the contact between the SCR devices and the heatsinks must be as good as possible but over time, and especially in offshore installations, corrosion may attack the interface between the SCR device plating and the aluminium heatsink. If corrosion is present it takes an expert to decide if refurbishment is required because as long as the damage is minimal and the two elements remain undisturbed, the mutual corrosion may still maintain a good contact.

As part of the health check our engineer will do a sample inspection of the heatsinks and recommend a course of action based on experience and knowledge.

Click here to find out more about our bespoke SCR Health Checks and Timescales.

Repair & Calibration

Since our acquisition of Hill Graham Controls (HGC), our module repair facility and engineers, have been able to test and calibrate modules sent to us for repair within a quick turnaround period. In an important development, Zeefax has designed and built a new AC and DC Module simulator, to provide an improved testing platform for Hill Graham and Ross Hill type AC and DC modules. In particular, the AC module simulator is much improved over the older unit, and provides a greatly enhanced engine control and start-up simulation.

These improvements have been made based on our experience with testing and repairing the modules over many years, and our customers can be confident that any module returned to us for repair will receive the most comprehensive bench test possible.

In addition, we are able to repair and re-calibrate most Hill Graham and Ross Hill type printed circuit boards (PCBs), including Power Limit, Field Supply Regulator, Sprocket Slip, Drillers Console, DC Auxiliary, SCR Auxiliary and Generator Exciter PCBs. Furthermore if following evaluation, repair is not possible, in many cases we can supply new manufactured boards using the original designs, but enhanced by us using modern components and manufacturing techniques. In this way, we can help to ensure that legacy systems remain operational and continue to provide reliable and trouble free service beyond their expected life.

Motors & Generators


  • High Torque DC Motors ranging in size from 7.5 HP up to 35,000 HP
  • AC induction motors, also with Thermalasatic Epoxy Insulation
  • Horizontal & Vertical Squirrel Cage Induction Motors
  • Induction Motors for pumps
  • Synchronous motors ranging in size from 500 HP up to 30,000 HP
  • Oil well pump motors
  • Open Drip-Proof Motors
  • TEFC Motors ranging in size from 250 HP up to 1000 HP
  • Petroleum and Chemical Motors, designed for continuous operation or for long periods of inactivity in petrochemical plants.


  • Diesel generators for land rigs
  • Offshore and marine
  • Captive power systems
  • Governors and voltage regulators
  • Portable Power Control Rooms (PCRs)
SCR Pod Refurbishment

SCR Pod Refurbishment

Even given the relatively controlled working environment of typical SCR pods, the conditions can often cause deterioration to both electrical and mechanical performance, requiring removal of the unit from the system, followed by refurbishment and renovation.

During refurbishment, the pods are disassembled, checked and thoroughly cleaned; resistors and capacitors are replaced, and fuses, actuators and switches are checked and tested for operation, and replaced where necessary, and the pod is fully re-wired.

The heat sinks are inspected and if required, will be re-machined to ensure excellent electrical contact is maintained. Importantly, the SCR Thyristor ‘puck’ is replaced, and very special attention is given to the clamping torque and orientation.

When complete, a full quality inspection and electrical test is performed to ensure that the refurbished cell is in perfect working order prior to dispatch back to the owner.

Refurbish or Replace

We are also able to offer refurbished units, which can be held in stock for emergency spares or as replacements for units which are undergoing refurbishment at our factory.

If you would like to know more about availability of SCR pods, please call or email us, and we will be pleased to assist.

Foot Throttles

Foot Throttle Refurbishment

The severe environment on rigs often leads to a deterioration of both electrical and mechanical performance of Foot Throttles, requiring removal of the unit followed by factory refurbishment and renovation.

Typically, units arrive in poor condition – totally seized and unusable; they are then completely disassembled, thoroughly cleaned and de-scaled, and are fitted with new bearings, bearing blocks, hardware and seals, prior to re-wiring and calibration.

Zeefax is able to provide both factory refurbishment of existing Foot Throttles and in cases where the deterioration is too severe for refurbishment, we can supply a brand new replacement to meet specific requirements.

If you would like to know more about the range of available Driller’s Foot Throttles, please call or email us, and we will be pleased to assist.

SCR Blower Assemblies

Keeping the components cool

An important part of every system is the forced air cooling, which is vital to ensure continuity and reliability of operation of the SCR stacks. It is essential that the heat generated during operation is reliably carried away, and Zeefax now produce a series of SCR Blower Assemblies which are compatible with the those used in legacy Hill Graham and Ross Hill type systems.

The Zeefax SCR Blowers are designed to operate with voltages up to 600 V @ 50 or 60 Hz; the operating voltage needs to be specified at the time of purchase (see the details and specification form below) and the blower may be configured with either Single or Duplex impellers and with or without base frames.

The Zeefax SCR Blowers can be used to replace faulty or broken blowers with confidence.


Blower details and specification form

In order to aid potential users with the selection of replacement blowers, we have created a simple form which can be used to provide the few technical details we require. In this way, we can ensure that any SCR Blower supplied by us is fully compatible with existing assemblies, and will then install directly into the available location with minimal re-work required. You can download this form from this site; please fill it in and return it to us to receive a quotation.

If you would like to know more about the range of available blowers, please call or email us, and we will be pleased to assist. Click here to download the fillable details form.

Printed Circuit Boards (PCBs)

Re-engineered circuits boards

Where an exact replacement is not available due to limited supply or obsolescence, Zeefax can re-engineer an alternative or recommend a suitable equivalent.

Through our in-house R&D, we are developing improved specification products as replacements for legacy Hill Graham Controls or Ross Hill Controls boards; we can provide original replacements for many of the PCBs used on these systems, and by using modern techniques and components, we can even improve on some of the design features of the original products to enhance reliability and functionality.

This means that equipment manufactured up to 30 years ago is still fully supported by Zeefax, and can continue to provide a return on investment well beyond the normal life expectancy.

PLC Training Course Program


Our PLC training program is held at our modern product development and production facility, located in Bracknell, near London.

During the course, we aim to provide students with an advanced training experience, enhancing the already popular series of PLC training courses provided by Zeefax.

This training course includes modules for both novice and advanced users of PLCs, and includes information and techniques for manufacturers including AB, GE Fanuc, Mitsubishi and Siemens. Courses are intended for both technicians and engineers who wish to expand their skills and knowledge of PLC programming, fault finding and maintenance.

Course programs and content may be tailored for specific requirements and needs, but will typically focus on the more practical aspects of Programmable Logic Controller applications.

At the end of the course, engineers and technicians will be familiar with the program modules and functions, and will be able to fault-find on PLC controlled plants.