When the lights go out and the cups fall off

A smaller (about 2.5kVA) generator will power essential appliances one or two at a time, depending on their load. So in turn, the freezer, fridge, water pump, etcetera can be run. Generators of this capacity will cost $500 to $1300. A higher-capacity 4kVA generator at a cost of $1300-$2000 will allow more appliances to be run simultaneously. The decision on capacity should be based on expected frequency and duration of power cuts, and level of convenience expected. Hiring a generator is another option, but during severe weather conditions they might be in short supply, and roads blocked, or there might be more pressing issues to attend to.  
There are a lot of features to consider when choosing a generator for the house.
Capacity: This is usually rated by kilovolt amps (kVA), a measure of the apparent power, and is a product of the voltage and current. Single-phase generators commonly range from 0.5 to 11 kVA. Some suppliers rate their generators in kilowatts (kW), which is a measure of the power available for use. To convert kVA to kW, multiply kVA x 0.8. Specs might include a figure for “Rated Output” which is the optimum output for the generator. They might also quote a maximum output. The horsepower quoted for generators refers to the power rating of the engine driving it. Remember when considering generator capacity, that some appliances with motors require several times more power for start-up, than for running.
Standard or Inverter generator: Inverter generators produce cleaner power (smoother and more consistent) than standard generators and are suitable for sensitive equipment like computers. They can cost twice as much as standard generators, for the same capacity.
Continuous running time: The time the generator will run for on a tank of fuel, and might be quoted at a specific load.
Starting system: Pull or electric start, usually with back-up pull starter.
Engine characteristics: Fuel type, power rating, and displacement.
Fuel tank capacity: Litres of fuel capacity.
Automatic low oil shutdown: Prevents engine damage if the oil level drops too low.
Circuit breaker protection: Prevents overloading of the generator.
Automatic Voltage Regulation (AVR):  Regulates the output at 230 volts, so more stable power with fewer surges and dips. While computers can be run by standard generators with AVR it is wise to have surge-sag protection for sensitive electronic equipment.
12 volt DC outlet, 230V AC outlets.
Voltmeter: To allow monitoring of output voltage.
Sound level: The generator could be running overnight close to bedrooms. Sound levels in dBA are commonly quoted for generators. Some are silenced.
Complementary functions: Some generators double as a portable welder. The Gruppi Elettrogeni Four-In-one is a 5.5kVA generator, 180amp welder, 2030psi water blaster, and 340l/min compressor in one package.   
Generators for the dairy are three-phase, and can run three-phase and single-phase equipment. An electrician or generator specialist can advise on capacity requirements, based on the starting and running wattage of the equipment to be powered. They can also help with sourcing a suitable generator, installing it, and making the appropriate mains connections. The electrician must take account of electronic equipment like variable-speed drives in generator selection. Other considerations include the engine (perceived quality), alternator quality and operating specifications, sound level, weather resistance, general engineering, service and maintenance requirements and safety aspects.
Generators to power the dairy can be PTO-driven, portable or stationary.
PTO-driven generators come in a range up to 100kVA, big enough to power any modern farm dairy. A PTO-driven generator can be used at other sites around the farm, but when in use they tie up a tractor at a time when tractors may be in demand. Maintenance is minimal because there is no engine with the generator.
PTO-generated power is often not as smooth as that of portable or stationary generators, so it’s not as suitable for sensitive electronic equipment. Where this is running, it must be protected by a suitably sized UPS. A unit with a four-pole 1500rpm alternator is most suitable. Automatic voltage regulators are an integral and standard part of all generators.
“Look for analogue needle voltage and frequency meters which are easily seen from the tractor cab, rather than a series of LED lights, to make set-up easier,” Mitchell Day of Pace Power and Air, New Plymouth says, “and a good solid PTO frame as there can be some vibration.”
PTO generators must be run at the correct PTO speed, to produce 50hz power. Increasing the PTO speed to compensate for an undersized generator or undersized tractor will increase the frequency above 50hz, which can damage the equipment being run. The tractor HP rating should be about twice the generator kVA rating.
Larger motors driving vacuum pumps and washdown pumps should be fitted with a soft start to minimise the voltage drop at start-up. Alternatively, a larger generator will compensate for start-up requirements. Some modern tractors have regulated PTO speed which is a definite asset for running generators.
PTO-driven generators are generally much cheaper than engine-driven generators of similar capacity. Expect to pay about $8500 for a PTO 65kVA generator, compared to about $20,000 for an engine-driven version.
Portable generators can be bought, or hired when needed if available and accessible. Like PTO generators they can be moved to unpowered sites for construction work, and moved between farms and houses. Some farmers have shared ownership with neighbours. They are usually trailer-mounted. Their capacity range is up to 100kVA, which will power the biggest of dairies. Most are powered by diesel engines. The power produced by these generators is smoother than that of PTO-driven generators.
Look for a system with a reputable engine and alternator. If the unit is to operate in dusty conditions, then a good filtration system on the alternator will increase its life expectancy.
Stationary generators tend to be larger-capacity units which can power a larger dairy and houses, or are found where temporary power must be provided as soon as the local network cuts out. They are hard-wired in to the switchboard and can be programmed to cut in when the mains power fails. Stationary generators are similarly priced to portable units.
Connecting a generator to run a farm dairy will require electrical work at the switchboard, which is likely to cost $2000-$3000. This includes a suitable capacity plug for PTO or portable generator leads, or wiring in a stationary generator. It also includes a transfer switch. This is a fail-safe means of isolating the dairy from the local supply before the generator can feed into the switchboard. This prevents any chance of electrocution if someone assumes the lines are dead. The plug must be connected after the meter so the farm is not charged for the power generated.
Farmers must do their bit to reduce the chance of power cuts by keeping trees clear of power lines. Guidelines on clearances between trees and power lines is available from lines companies. Some provide assistance in removing or trimming trees close to power lines.
Well prepared
Braeside Dairies, owned by Braeden and Caroline Whitelock, is well-prepared for power cuts. The dairy farms at Linton in Manawatu are certainly not in the back-blocks, but are near the end of a line in terms of power supply.
Koteka Electrical installed an Olympian GEP165 generator when their 80-bail rotary dairy was built in 2009. Twelve hundred cows are milked through the rotary, with another 600 being milked at an adjacent farm. The 165kVA generator is capable of running the rotary, a mid-size herringbone on the same farm, and two effluent irrigators simultaneously.
Switching to generator power is straight-forward. First the generator is started. The farm is isolated from the local supply with one switch, and then connected to the generator. A single key for both switches means the generator can’t power the farm while it is connected to the local supply. Switch-over takes less than a minute, and none of the electronics in the dairy, such as the Smart-Air vacuum pump controller or the computer, need resetting.
The generator to date has been completely trouble-free and requires minimal maintenance. It is used to power one milking every month, as part of its test and maintenance procedure.