ROSS HILL BOMAY CHINA

It is an unfortunate characteristic of SCR systems that the Power Factor (the relationship between real and reactive power) is poor – often down as low as 0.4 – which maeans that the KW capacity of the engines is under-utilised. This often leads to frustration because the rig runs out of power, yet the engines may be only delivering half of their full-load capacity. This article explains how the Power Limit system works and what can be done to ensure it is working at its optimal level.

In general terms, the KW the system consumes is provided by the engine. The other limitation on power delivery is the current capacity of the generator, which is often expressed as a VA or KVA value. SCR systems are designed with something like a 0.7 Power Factor rating; in other words, the KW of the engine will be 0.7 x the KVA rating of the generator. This goes some way to compensating for the poor Power Factor, but often is insufficient during operations where where the Mud Pumps are heavily loaded. However, measures are still available to ensure that the system is delivering what it can within these physical limitations, one one thing to ensure is that the Power Limit system is working optimally.

The purpose of the Power Limit is to prevent rig blackouts in the event of sudden increases in load. The original philosophy also was to allow the minimum number of engines to be run and maximise efficiency but most drilling operators prefer not to run up against these limits and demand as much power as is available. The Power Limit system measures the KW load of the highest loaded engine, and the current load of the highest loaded generator and compares this to a pre-set reference to determine if Power Limiting of the SCRs should occur. Furthermore, some systems have an initial 60% KW limit, which then opens up to 100% once this threshold has been reached under ramped control. This is to allow the engine turbo-chargers to spin up. Once above this threshold only the 100% limit is in operation, unless the load dips below 60% in which the ramp is re-set.

One other addition to the basic Power Limit is a 90% switch setting, which reduces the overall KW limit to 90%. The thinking here was to compensate for engines which had become old and a bit tired or due a maintenance overhaul.

The Power Limit system ONLY affects the SCR output; there is no control over other AC loads.

Power Limit Calibration

It follows, therefore, to ensure the Power Limit card is correctly calibrated. The procedure for calibrating the Power Limit system is beyond the scope of this article, and should not be undertaken by unqualified personnel. This is a job for your service engineer. For a typical system with CAT D399 engines, the engine will have a 930KW rating, and the generator will be rated at 1500KVA which equates 1443A maximum load. When fully in Power Limit, at least one of the generator section meters should show either maximum KW (930KW in our typical system) or maximum current (1443A in our example). If not, there may be a problem with the calibration of the Power Limit system, but there may not – the calibration may have been set deliberately low to compensate for equipment which is a bit old and tired and can’t quite deliver nameplate ratings.

Hopefully, when the rig is fully loaded, the load will be shared equally amongst the engines and generators. All the engines should have KW values within 50KW of each other. The generator KVAR meters should also be showing values within 50 KVARs of each other. If not – remember that the Power Limit system only looks at the highest loads – it will be the highest loaded engine or generator (they may not be the same unit) which dictates when Power Limit occurs. The KW load sharing is usually not adjustable, but it is absolutely vital that, when a generator is put on line, the voltage adjust potentiometers are adjusted to balance up the KVAR. Once adjusted they should remain balanced unless there is a problem with the KVAR/voltage regulation on any one generator which may be caused by a faulty exciter or exciter controller. Either way, if load sharing is poor, Power Limiting will prevent the rig developing full power.

Power Factor Correction

Power factor correction has been deployed on a number of systems in the form of capacitor banks to compensate for the poor power factor. Although this might make the numbers look better, there is some doubt as to whether or not it increases the useable power from the limited amount of generating capacity available. About 1500KVARs of reactive load is required to make a significant difference.

ROSS HILL SCR BOMAY

DSL is a team of experienced electrical engineers with over 15 years experience in electrical design, manufacturing and commissioning.

We design, deliver and support electrical engineering projects, from simple machine controls to large scale production and process line systems. Our key skills include:

ROSS HILL Spare Parts

Spare Parts

JOTON has forged relationships with many of the worlds leading industrial equipment suppliers and, together with it’s own technical and manufacturing capabilities, can source or manufacture a wide range of spare parts for Westinghouse, GE, Ross Hill and Hill Graham SCR systems.

We are able to identify Ross Hill or Hill Graham parts from the original part number, and can provide exact equivalents where these are available. Where an exact replacement is not available, either due to limited supply or obsolescence, Zeefax can engineer an alternative or recommend a near equivalent.

This means that equipment manufactured up to 10 years ago is still fully supported by DSL, and can continue to provide a return on investment well beyond the normal life expectancy.

AC & DC Control Modules

DSL can provide you with exact replacements for your Hill Graham or Ross Hill systems. We have built a unique database of these specifications, and this, combined with the experience and expertise of our technicians (former employees of Hill Graham in the UK) enables us to re-engineer, and even improve on, the original specification.

We believe we are the only company in the world able to provide replacement AutoSync modules for Ross Hill and Hill Graham systems. In order to improve on the original design, this product is fully digital, but is an exact replacement, occupying the same footprint and having the same pin configuration.

Printed Circuit Boards

DSL are today developing improved specification products as pin-for-pin replacements for legacy Ross Hill and Hill Graham technology. We can provide many of the printed circuit boards used on these systems, and even improve on some of the design features of the original product to improve reliability, robustness or functionality.

Thyristors, Diodes and Fuses

Advancements in technology mean that many of the power semiconductors which were built in SCR systems 10 years ago have been superseded by devices with better specifications. Specifying replacement or equivalent devices is a skilled task, but 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.

Repair and Calibration

DSL has designed and built a new type of AC and DC Module simulator, both provide a better testing platform for standard Ross Hill and Hill Graham type AC and DC modules. In particular, the AC module simulator provides a much improved engine control and start-up simulation.

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

In addition we are able to repair and re-calibrate most Ross Hill and Hill Graham printed circuit boards (PCBs), including Power Limit, Field Supply Regulator, Sprocket Slip, Drillers Console, DC Auxiliary, SCR Auxiliary and Generator Exciter PCBs.

ROSS HILL Surge suppression circuit

All these over-voltage refer to peak voltage, but SCR elements are damaged, which are usually eliminated by using varistor, namely the surge suppression circuit.

Composition of system elements: varistor, fuse and indicator light.

ROSS HILL SCR entire bridge flow

Composition of system: silicon control, radiator, fuse, chocking winding, pulse transformer, RC absorption, axial-flow fan, 1200ADC/1800ADC DC contact/1200ADC commutation contacts and circuit breaker.

ROSS HILL Power limit box

Main functions:

Power limit value can be freely set from panel from 80% to 110%. When active power (KW) reaches 95% of the set value, indication light will display; when active  power (KW) reaches 100% of the set value, output OVDC to ensure driving system can not continue loading.

When total current (I total) reaches 95% of the set value, indication light will display; when active power (I total) reaches 100% of the set value, output OVDC to ensure driving system can not continue loading.

When frequency is lower than 48HZ, indication light will display to ensure driving system can not continue loading.

When speed rate of load sudden change exceeds instinct character of diesel engine, load loading time will be postponed to ensure stable operation of diesel generator set.

ROSS HILL Excitation circuit board

Main functions:

Convert AC voltage that the generator produces to DC voltage needed by generator excitation machine. The board consists of two rectifier circuits: One is bridge rectifier and the other is silicon controlled rectifier. And both are automatically conversable.

When generator starts, bridge rectifier circuit can rapidly build voltage for generator without requiring externally connected battery box accessory due to low remnant voltage of generator.

When voltage of generator rises up to a certain voltage, silicon controlled rectifier circuit will automatically replace bridge rectifier circuit seamlessly to ensure safe and reliable excitation circuit of generator.

When generator operates normally, the voltage of generator that internal loop that constitutes closed-loop control with AC module maintains is 600V AC.

When load of generator set changes suddenly, it constitutes a external loop with AC module to stably regulate exciting voltage for rapid restoring voltage set-point.

ROSS HILL Ground fault circuit board

Main functions:

When any one item outputted by generator is shortly connected directly or indirectly, the corresponding indication light will be more bright (dark bright at normal condition) and AC ground percentage meter indicates ground degree.

When SCR positive and negative busbar outputted by cabinet is shortly earthed directly or indirectly, the indication light will be more bright (dark bright under normal condition) and DC ground percentage meter indicates positive or negative end earthing, which indicates ground degree.

Composition of system elements: Ground testing board, AC/DC percentage meter, indicator light, reset testing switch, resistance and insurance, etc.

ROSS HILL HOC circuit

Main functions:

When the first diesel generator set starts, it provides control module with working power.

When the last diesel generator set is disconnected from the networks (CB disconnects) and after voltage reduces to 220VAC, it provides control module with working power.

Composition of system elements: voltage transformer, rectifier bridge, capacitance, resistance, voltage regulator diode and 12VDC battery jar.

ROSS HILL Current demodulation board

Function of current meter demodulation board:

Mainly finish ammeter’s matching with transformer output current of generator 3-phase AC. Namely,5AAC input is transformer into 1Ma DC

ROSS HILL frequency meter filter board

Function of frequency meter filter:

Reduce influence of harmonic component on frequency meter to make frequency meter work accurately and stably.

ROSS HILL AC control module

Main function:

Finish double close-loop control of diesel motor unit and voltage with high control accuracy and smooth change (50HZ/60HZ) and finish various protection functions of diesel motor and generators.

ROSS HILL DC CONTROL MODULE

Modern Drilling practices demand additional mud pumping capabilities which was not envisioned in older systems. JOTON can revitalise a rig by adding a third Mud Pump and add-on mini console.

We can also conduct a power study on your rig to see where extra capacity can be added, and make recommendations on how this can be achieved.