Self-Power Generation in Industries – Applications, Issues and solutions

The availability of stable & reliable power is the basic necessity for Industrial & Economic growth. Pakistan, with the 5th largest population in the world and with the availability of abundant natural resources should have developed its industries much better than where it is today.

However, without involving in any political debate, let’s come to our title topic. I will try to share the concept using simple wordings so readers can understand without knowing specific technical terms.

Self-Power Generation:

During the early 2000s when Naturals (CH4) was made available for commercial & industrial users in Pakistan, almost entire industry shifted to Self-Power Generation, as the cost of Self-Power production was significantly low compared to purchasing power from Utility Grid. While Self-Power Generation was reliable too as compare to Utility Grid.

Let us understand a bit more about Self-power or Captive Power Generation. If we talk about small to medium-sized industrial units, the power consumption requirement varies from few MW to 50MW at max. Due to the size of Industries and their load requirement, they ideally need generators with individual capacity from 1MW to 5MW.

Both Diesel & Gas Generators are available in this range. However, because of the expensive cost of diesel fuel, Diesel generators are not a viable option for continuous power generation in industries. However, all industries & Commercial complexes i.e. Hospitals, Hotels, Malls, etc. do install Diesel Generators for an emergency supply of power, in the case; a) the main Grid supply is interrupted, which might be due to technical fault or natural disaster/accident; or b) shortage of natural gas (CH4) pressure which might not be enough for self-power generation using gas generators,

So, the Generators which run on Natural gas, biogas, landfill gas, etc. are ideal to run continuously 24/7, to cater industry’s power requirement and can replace utility Grid. When the customer becomes self-sufficient for his power needs through his own Power Generation, we called it Self Generation / Captive Power Generation. In some cases, one industry also sells the power to nearby industrial units, in this case, the power plant can be termed as Micro Grid. 

Gas Engine Manufacturers:

Unlike Diesel, the number of players in Gas Engine manufacturing is limited because of extensive, expensive and continuous R&D while the nature of the product is also quite complex. Some of the pioneer companies in Gas Engine manufacturing are Cummins, Caterpillar, and Waukesha, Some other companies which have earned name globally include Waukesha, Rolls-Royce (MTU), and Jenbacher.

Remember that Gas & Steam Turbines are different from Gas Generators. The Turbine normally starts at 5MW and can go up to 200MW. They are used for large scale power production and mostly used by IPPs who sell power to Utility companies.

What Features Industries look when buying Gas Generators?

So, coming back to small & medium size industries and especially for the Pakistan market, With the availability of GAS, Industries bought Gas Generators 1MW, 1.5MW, 2MW, 2.5MW, 3MW, 4.5MW, etc. and continue to add Generators as their demand increased over the time. With more than one choice available for an industrialist in the brand of Gas generators, some companies tried new brands every time they went for expansion.

When buying Gas Generators, the customer makes the selection based on his priority requirement. One Gas generator cannot fulfill all the requirements. Some generators are designed and known to be successful in their specific characteristics. Some of the major features are as below:

·        Step Load Capacity: This is one of the unique requirements in a specific industry where they have frequent & sudden changes in the load. It may be due to the type of process where certain motors start & stop with intervals. Cummins QS Series is known for heavy torque load capacity.

·        Consumption of Gas: Where the customer load is stable & engine is running 24hrs then the customer’s preference is the lowest Gas consumption on the same KW output. In Pakistan, mostly process industries like textile, cement, pharma, food & beverages, hospitals, etc. look for these types of Generators. Caterpillar 3500H Series engines, Caterpillar CG Series engines & Jenbacher engines have been supplied well for these applications in the Pakistan market. Also, MTU Brand supported by Rolls-Royce engine has just entered in this segment in Pakistan Market.

·        Reliability & Availability: Where the customer is having harsh ambient environment and Gas quality is not pure, the engines with robustness are preferred over an efficient but sensitive engine, mostly Oil & Gas companies look for these kinds of engines. Caterpillar 3500 Series and Waukesha Generators are known to operate in these conditions.

·        Type of Load: Type of load varies in each industry depending on its process. We can categorize loads in two basic types - Linear and Non-Linear. Examples of linear loads are lights, synchronous motors, electromagnetic devices, resistors, heaters, etc. While non-linear loads include Rectifiers, Variable Frequency drives, Uninterruptible Power Supplies, Battery charges, fluorescent bulbs, etc. Every manufacturer studies the customer’s load profile and accordingly makes the selection of a suitable series of the Gas engine from their available models. 

Gas Engines are producing continuous Power but what more issues Industries have to face?

Now, Gas Generators are installed and producing power continuously but industrialists want to address following additional concerns:

1-     How power can be made available when the Gas Engine is down due to maintenance or fault?

2-     How power can be made available when Gas Engines are not running because of the unavailability of Gas.

3-     How to cater loads that have a specific characteristic that cannot be served with Industrial Gas Generators?

4-     How can the industry further improve its power generation cost?

Before we answer the above questions, we should know that when Generators are utilized for Power Generation in industry, they are categorized in the following four types based on their operating hours:

How do we classify Generators based on their operating time?

·        Continuous Power Generators:  Generators that function as the main source of power and are designed to operate continuously at a constant load for an unlimited number of hours with maintenance intervals as per manufacturer recommendation.

·        Prime Power Generators: Generators that function as the main source of power and are designed to operate continuously at a variable load for an unlimited number of hours with maintenance intervals as per manufacturer recommendation. Continuous and prime power generators are very similar as both function as the main source of power and are designed to operate continuously or for extended periods of time. The major difference between the two is that continuous Power generator sets are designed to operate with a consistent load while Prime generators are designed to operate at variable load.

·        Emergency Standby Generators: Generators which function as back up source of power, they are designed to operate for the limited number of hours with maintenance interval as per manufacturer recommendation. They operate in an emergency situation when the main source of power is not available for any reason.

To address concern no. 1 – How power can be made available when the Gas Engine is down due to maintenance or fault?

The customer may install Diesel Generator which runs as Emergency / Standby Power. Let say one customer has load requirement of 6MW and he has 3 x 2MW Gas generators available, he may install one x 1MW Diesel Generator as Emergency standby, if one Gas Generator is down, some non-essential load will be out of power and remaining will be served through standby Diesel Generator.

To address concern no. 2 - How power can be made available when Gas Engines are not running because of the unavailability of Gas.

Many customers had faced this problem in Pakistan, during the winter season especially, they cannot afford 100% backup arrangement through Diesel Generators, therefore they need to purchase power from utility Grid, and they only use Grid power when Gas Generators are not available.

To address concern no. 3 - How to cater loads that have a specific characteristic that cannot be served with Industrial Gas Generators?

Every industry does its load analysis and if it is known that expensive Gas Generators can be damaged with a certain non-linear load than customer brings the Grid Power supply in parallel to Generators and all those variations are catered by Grid Power.

To address concern no. 4 - How can the industry further improve its power generation cost?

This can be done by efficient Power Generation Control System, where Grid Supply, Gas Generation, Diesel Generation and now Solar Power are used in most optimum combinations where operation cost, maintenance cost and reliability of the system is ensured.  

Why Industry Need & Utilize different Power sources i.e. GRID, GAS / DIESEL GENERATORS AND SOLAR?

Utility Grid Power: Grid supply is preferred when it is less expensive compare to own power Generation. It opts when a certain kind of non-linear load or heave torque load cannot be catered by Generators. It is also used as backup power when prime power Gas Generation is not available. The Grid supply can also run in parallel with own Generation when load requirement exceeds Self Generation.

Gas Generators Power:  When Gas is available, the customer would prefer all Gas Generators should be maximum utilized first, as Self Generation is less costly, and its power quality is better & more reliable compare to utility Grid.

Diesel Generators Power:  They are mostly used as standby, also in some cases of a complete blackout of the plant, Diesel Generators are used to startup, which is why they are also called black start Generators.

Solar Power:  Now, every industry is putting solar power at least to cover 15-20% of the load demand. Although the capital cost of Solar power is higher than Gas Generators. However, its operation cost is much lower than Gas Generators and the life cycle is much more than Gas Generators.

Since solar power is mostly available in the day time, a maximum of 8 hours, it is used as a mean to reduce overall power Generation Operation cost, however, the customer may continue to require other constant power sources like Gas Generators & Grid to have power available around the clock.

If you have read the article up till now, you would have ample understanding of what is Self-Power Generation, what are its problems and needs? Now, understand one important part “Central Power Control System”.

Role of Central Power Control System in Modes of Operation of Generators:

This is like the brain of Self-Power Generation, which automatically achieves all discussed power source management functions. We illustrate with examples,

1-     If the customer has only one Generator sufficient for its entire load than it will run stand-alone to serve the load, the technical term used for this application is Island Mode.

2-     If the customer has two different brands of Gas Generators, they should be able to share the load according to their capacity. Example - 2MW & 1MW generators should take up to 1.66MW & 0.83MW load respectively out of total load requirement of 2.5MW, the technical term used for this application is Load Sharing.

3-     However, if the customer has the same two Generators, where 2MW is brand new and 1MW Generator is Old, the customer wants to utilize maximum power Generation from 2MW Generator as it consumes less Gas giving same power compare to 1MW engine. Thus out of 2.5MW load requirement, brand new will serve 2MW while old one would cater 0.5MW, the technical term used for this application is Baseload operation (when one Engine run on fixed power KW output in parallel with other Genset)

4-     Only the minimum number of Generators should run at a time as per the load requirement. For example - if there are 2MW, 2MW & 1MW generators installed and load requirement is 2.8MW then one 2MW generator should remain OFF, while if load requirement is 3.5MW then 1MW generator should remain on standby, the technical term used for this application is Load sense/ load demand management. 

5-     Grid utility should be able to run with Generators in parallel for long hours, called Generator-Grid Parallel operation[S1] [S2],  both Grid & Generators supply can be brought on the same BUS in two cases:

a.      If the load is running on Grid supply and it is known that Grid supply will be interrupted at a certain time, or if the rates of Grid supply will become high at a certain time, then control system automatically starts Gas Generators & parallel it with Grid supply, the technical term for this application is called Forward Synchronization.

b.     If the system is running on Gas Generators and Gas shutdown is to occur or Gas engines are to be taken on maintenance, then the control system automatically close Grid breaker to run both Gas Generators & Grid supply run in parallel, the technical term for this application is Backward Synchronization.

6-     Similarly, if the customer wants to switch over from Grid to Generator power or vice versa, not intended to run both in parallel for a long duration then the control system will make it possible without power interruption, the technical term used for this application is Close Transition Switching or ZERO Power Transfer.

Generator Control Module and its Function:

It is the heart of Central Power Control System, Generator Control module is responsible for all the modes of operations discussed above, Generator modules are installed one each against Gas Generator, Diesel Generator, Utility Breaker, BUS Coupler Breaker, Solar Breaker, etc., These Generator Control modules are connected with each other via CANBUS or through 0-3VDC analog lines. Each Generator control module communicates to its respective Generator Governors & Generator AVR to control Fuel and voltage output respectively. (Ref Fig- GCM Synchronization, Fig-GCM Load Sharing)

All the discussion of power plant management & its controlling is incomplete without a clear understanding of some basic technical function, Synchronization is one of them. 

What is Synchronization and how it is done?

To bring two sources of power parallel, we need to ensure the following parameters on each side of the BUS are same before closing the middle Circuit Breaker.

·        The voltage of both sides should be within the same allowable window (it is achieved by a command to Generator AVR from Generator Control module)

·        Frequency of both sides should be within the same allowable window (it is achieved by a command to Generator Governor from Generator control module)

· Both sides of the BUS should have the same phase sequence & Phase angle. (Same Phase sequence is ensured at the time of cable installation by connecting R, Y, B in the same sequence for both sources)

Thus synchronization is the process of changing parameters (refer above) of one side of BUS in comparison to the other side and closing the middle circuit breaker to bring both sources in parallel.

What are the main functions of the Generator Control Module (GCM)?

Before the invention of microprocessor relays, we had electromechanical devices and each device performs only one function, however with these microprocessor-based Generator control modules, we have the luxury for many additional functions, apart from the prime function of synchronization, which are as below.

1-     Synchronization – As stated above, GCM achieves this by controlling the voltage, frequency and phase angle through AVR and Governor of its Generator in comparison to the Master source Voltage & Frequency. (Ref Fig- GCM Synchronization)

2-     Electrical Protection – GCM receives the signal from Voltage Transformers on both sides of the Circuit Breaker BUS and current Transformer from one side, these Current & Voltage inputs help GCM do the synchronization and electrical protections of the Generator.

3-     Load Sharing & Control – In order to run Generator in different modes, like baseload, load sharing, import/export control, peak shaving, etc., GCM achieves this by controlling the AVR and Governor as stated earlier. (Ref Fig- GCM Load Sharing)

Master source can be BUS running with multiple Generators or Grid, Here it is important to understand the following two concepts.

·        If we have to synchronize two Generators or one Generator with Multiple Generators then one Generator becomes a slave and follows the voltage & frequency of the Master BUS.

·        If we have to synchronize one Generator or multiple Generators with Grid then Grid will always be the Master source as we cannot adjust voltage & frequency of Grid. If we have multiple Generators to synchronize with Grid then we add one Utility Control Module or Mains Control Module which senses the Utility voltage & frequency and conveys the feedback to all Generator control modules connected with every Generator.

Generator Control Module (GCM) brands in the Market:

Since Gas Generators run 24/7, therefore every Gas Generator manufacturer does offer their own Generator Control Panel, however, when two different brands of Generators need to synchronize and load share, it is preferred to have a similar brand of Generator control modules control each Generator.

Mostly Gas Generator manufacturers have origin from the USA while mostly GCM manufacturers have European origin, The famous brands available in the market for Generator Synchronization modules or Generator Control modules are WOODWARD, DEIF, ComAp, Deep Sea, Sices, etc. The working principle of every Generator module is the same but they vary in terms of additional features and hardware durability.

What is the Master Control Panel & its need?

There are certain functions required in controlling of the complete power plant, like monitoring of mechanical parameters of the engine, alarm logging, fault recording, trending of Electrical parameters, historical trending of the data and its visualization on Human Machine Interface, communication of data to the bigger central SCADA system, visualization of the complete plant in customized user-defined view, load shedding system in stages in case of failure of power sources.

To achieve all these functions, normally programmable logic Controls (PLCs) are added with Generator Control modules, where Generator modules are responsible for Synchronization, load sense load demand, load sharing management while PLC & Human Machine Interface is responsible for other additional stated functions, the common term used for this central PLC-based control is Master Control Panel.

Benefit for Central Power Control System:

Thus an efficient Powerhouse control, management, and monitoring system will ensure that customers will get uninterruptable power means no loss in production and higher revenues for Industrialists.

It also ensures that power output is optimized and produced at the lowest possible cost and thus giving a quick and maximum return on Customer investment.

If you have any questions on the topic, you can write to me at [email protected]