Selecting a pump for a project is a team effort: the more the user can tell about his requirements (i.e. flow, head, levels, alternative duties), the easier it is for the supplier (and the user) to select the correct equipment. Here is a piece written by Gerhard Botha of New Way Power Systems – points to guide a “successful engine-driven generator application”. Write to him at wollies [at] newway.co.za.
Considerations for proper hardware selection, from the engine manufacturer’s perspective, to achieve a successful engine-driven generator application.
- A generator may be either AC (Alternating Current) or DC (Direct Current).
- AC generators are also called alternators and are now so common that “AC generator” and “generator” have become synonymous terms.
An AC generator produces electrical current by passing a conductor through a flux field. On 15KW and smaller generator sets, permanent magnets are typically used for the flux field, while larger sets use a DC current in field windings. The AC generator’s output current is generated when the armature windings cut the flux field. Regulating the DC current in the field windings, controls voltage.
Early AC generators used a fixed field and a rotating armature. The modern AC generators use rotating field windings with a stationary armature to produce output current. The rotating field is called the rotor and the stationary armature is the stator. An exciter generates the DC current for the rotating field. The exciter can either be static or rotating.
Three ways of sizing a generator set are: Peak Load, Motor Starting and Transient Response.
- When sizing for Peak Load, the installer calculates the maximum kilowatt electrical load and selects a generator set with equal or greater kilowatt capacity.
- To size an engine for Motor Starting, the installer determines the maximum motor starting current (inrush current) together with any other loads and selects a generator set with equal or greater kilowatt capacity. Since typical motor starting current is five times running current, maximum voltage dip occurs during motor starting. Smaller generator set sizes can be used when motors have sequential starting or use reduced voltage starting. Sequential starting spreads out the inrush load of several motors, while reduced voltage starting lowers individual motor starting current. Transient response sizing is based on the ability of the generator set to accept a load and recover to normal frequency and voltage within a specified time.
- Transient response is typically checked by block loading the set with a load bank.
The customer must specify the limits for maximum voltage dip, recovery time and power factor.
When an AC circuit is composed of a pure resistive load, the current wave is in phase with the voltage wave. With a pure inductance load the wave lags the voltage wave by 90 degrees. A pure capacitance load will have a current wave that leads the voltage wave by 90 degrees. The inductance and capacitance waves do not consume engine power, but they do increase the current flow in the generator and are measured by the ammeter. For this reason inductance and capacitance are sometimes called “reactive” power or “wattles” power.
Watts or kilowatts are real power. With a resistive load, watts equal volts times amperes. If inductance or reactance is in the load, the current will be higher, so multiplying volts times amperes gives a result that is more than the real power. Therefore volts times amperes is called apparent power and is measured in kilovolt-amperes or kVA. Real power (kW) divided by apparent power (kVA) is the power factor or PF. Technically PF equals cosine q, where q is the phase angle between the voltage wave and the current wave.
- kW = Real Power= kVA x PF
- kVA = Apparent Power
- PF = kW/kVA = Real Power/Apparent Power
The typical generator set runs at less than its full capacity most of the time. As the load decreases, the operating efficiency of the engine decreases which increases cost per produced kilowatt. This is not a major concern for Standby generator sets. However, the increased cost of operating Prime and Continuous systems at decreased loads can be significant.
Part load operation also allows unburned fuel to gather in the engine exhaust and lubrication systems. This type of operation can result in unsightly leakage from the exhaust system, as well as increased maintenance costs. An oversized engine will more likely have these problems. A generator set operates best from 50% to 90% of full rated load. Long-term operation at less than 30% of full load is not recommended.
Single phase and three phase power
- Single phase (1f) AC consists of either one or two voltages in series with exactly the same phase relationship. Single phase AC supplies power over two or three lines.
- Three phase (3f) consists of three separate voltages spaced 120 electrical degrees apart, using three lines plus a neutral line. The phases are usually given letter designations (Phase A, Phase B, Phase C). Not two phases are at zero voltage at the same time. No two phases are at peak voltage at the same time.
Standby generator sets are exercised on a regular basis to ensure readiness when needed. Exercising for short periods of time with no load is detrimental to the engine. The engine is best exercised when run for 30 minutes or more with 50% to 75% load. This allows the engine to run at normal operating temperatures.
Balanced three phase loads
Generators should have the resistive and inductive loads balanced on each phase. A phase imbalance of more than 5% will cause unstable voltage regulation. This problem cannot be corrected with engine or generator adjustments. The distribution circuits should be rearranged until balance can be achieved.
- Southern African Pump Systems Development Association (SAPSDA) http://sapsda.co.za
- Steel & Engineering Industries Federation (SEIFSA) Tel: 011 298 9400 www.seifsa.co.za
Training and research
Find the “Training” option at http://sapsda.co.za. In-house training on products and pumping systems is also done for staff and distributors by companies involved in this industry.
- Adendorff Machinery Mart www.adendorff.co.za
- Aesseal SA Tel: 011 466 6500 www.aesseal.co.za
- Agrimaster Tel: 021 859 1816/7 www.agrimaster.co.za
- All Power Tel: 041 451 3936 www.allpower.co.za
- Alrite Engineering Tel: 011 626 2580 www.alrite.co.za
- Atlas Copco Tel: 011 821 9000 www.atlascopco.co.za
- Automotive Equipment International (AEI) Tel: 011 474 7480 www.aei.co.za
- Barloworld Power Perkins Tel: 0861 100 190 www.bwep.co.za Diesel and gas engines supplied to the industrial, construction, agricultural, marine and electrical power generation markets. Based in Boksburg, they are responsible for providing parts, warranty, sales, service and technical support throughout the subcontinent.
- Brumby Pumps Tel: 083 612 0475 / 083 234 7302 www.brumbypumps.com
- B&S Commercial Power Tel: 021 981 6040 www.bspower.co.za
- Bundu Power Tel: 011 397 7373 www.bundupower.co.za
- Continental Genset Supplies Tel: 018 431 1817/8 www.continentalgenerators.co.za
- CRI Pumps Tel: 011 805 8631 www.cripumps.co.za
- Cyclone Industries Tel: 011 821 5900 www.cyclone.edx.co.za
- Deutz Dieselpower www.deutz.co.za Branch details on the website
- Dicla Tel: 011 662 1371 http://dicla.com
- DR Pumps Tel: 012 940 6872 www.drpumps.co.za
- Elsumo Tel: 021 875 5781 www.elsumo.co.za
- Ernest Electro Engineering Tel: 011 792 9550/1/2 http://ernestee.co.za
- Flexipump RSA supplies the irrigation pump “designed for the developing world”. See www.flexipump.co.za.
- Franklin Electric SA Tel: 011 723 6500 www.franklin-electric.co.za
- Generator King Tel: 086 111 3847 www.genking.co.za
- Genpower Tel: 0861 101 103 www.genpower.co.za (Honda generators)
- Gentag Tel: 018 431 0555 www.gentag.co.za
- GOSCOR Power Products Tel: 011 230 2600 www.goscor-power-products.co.za
- Grundfos Tel: 010 248 6000 www.grundfos.co.za
- Hoffmann Power Tel: 011 334 6573 www.hoffmannpower.co.za
- Hydro Solutions Tel: 012 807 3256 www.hydropumps.co.za
- Jaytrade Tel: 021 385 1652 www.jaytrade.co.za
- Kirsons Trading SA Tel: 011 553 6903
- KLB Engineering Tel: 011 668 1923/4 www.klbengineering.co.za
- KSB Pumps Tel: 011 876 5600 www.ksbpumps.co.za
- Maiden Electronics Tel: 011 468 1619 www.maidenelectronics.co.za
- McBeans Tel: 033 342 1541 www.mcbeans.co.za
- New Way Motor & Diesel Engineering Tel: 010 216 2600 www.newway.co.za
- Northern Generator Services Tel: 012 993 1426 www.northerngenerators.co.za
- Performa Pumps Tel: 011 845 1100 http://performapumps.co.za
- Pumps for Africa Tel: 010 594 0335 https://pumpsforafrica.co.za
- Perkins – see Barloworld Power Perkins
- Rapid Allweiler Pump & Engineering (Pty) Limited Tel: 011 573 7400 www.rapidpumps.co.za
- Seal Services & Industrial Supplies Tel: 011 393 1881 www.sealservices.co.za
- Southern Cross Industries Tel: 051 434 3861 www.southx.co.za
- Staden Borehole Pumps Tel: 051 522 0397/083 287 2026 http://stadenpumps.com
- Stewarts & Lloyds Tel: 0860 10 27 99 www.stewartsandlloyds.co.za
- Sub-Sahara Power Distributors Tel: 011 493 0773 www.sspd.co.za
- Sulzer South Africa Tel: 011 820 6000 www.sulzer.com
- Turfmaster (Pty) Ltd Tel: 011 730 3400 www.turfmaster.co.za
- Vac-Cent Services Tel: 011 827 1536 www.vaccent.co.za
- Verder Pumps SA Tel: 010 040 3356 www.verder.co.za
- Water Powered Technologies www.waterpoweredtechnologies.com Self-powered water pump
- Watson Marlow Bredel SA Tel: 011 796 2960 www.watson-marlow.com/za-en/
- Wilo South Africa Tel: 011 608 2780 www.wilo.co.za
- Zest Weg Group Africa Tel: 011 723 6000 www.zestweg.com
- ZM Pumps Tel: 011 240 6900 www.zmsa.co.za
Websites and publications
Visit the different websites mentioned in this chapter.
www.worldpumps.com covers developments in power generation, pulp and paper, food and drink, desaliniation – all the uses that pumps and generators could have.
Call 012 842 4017 or email iaeinfo at arc.agric.za for the following publications, available from the ARC-Agricultural Engineering:
- Petrol-driven irrigation pump for emerging farmers
- Petrol-aangedrewe besproeiingspomp vir beginnerboere
- A guide to manufacturing the kit treadle pump
- The topics of manure pumps (types suitable, considerations for pump installation etc) is dealt with in the publication Manure handling in intensive animal production units, written by HT Breedt, edited and revised by F Cilliers. Copyright. 2009. It is also available from the ARC-Agricultural Engineering.
Visit the website of the British Pump Manufacturer Association – www.bpma.org.uk.