Back in the day, when tube transmitters ruled the broadcast world, common practice was to have a big cooling fan moving outside air through the transmitter building connected to a thermostat.  Temperature swings of 30 to 40 degrees were common, however, the tube rigs could handle almost any temperature that didn’t melt plastic or freeze water. Today’s solid state transmitters are not that rugged.  They like to have there rooms around 70 degrees +/- 10 degrees or so.  Not to mention the other computer controlled equipment commonly found at a transmitter site.  Things like air chain processors, STLs, remote controls, etc.  So, lots of air conditioning is the norm, and with lots of air conditioning comes lots of maintenance. Air handler air filters need to be checked and replaced often.  Condenser coils seem to attract every type of flying debris on the planet and need to be cleaned once, possible twice per year depending on tree and weed species near the site.  Even with the preventative maintenance, occasionally things like this happen:

Of course, the entire cooling coil inside is frozen solid. This condenser is low on refrigerant, causing icing problems.  It has a slow leak somewhere and is about to be replaced.  Other reasons for this happening are malfunctioning or non-existent low ambient kit on the condenser fan.  Sometimes less than knowledgeable persons will install a 5 ton unit designed to run throughout the year but not take into account the effect of moving below freezing air at high speed across the coils.  ac unit not cooling the houseInsufficient air moving across the cooling coil will also cause this.  can an ac unit run without a filterInsufficient air flow can be due to plugged air filters or clogged fan/blower blades.using window ac unit indoors

This one is even better (same condenser unit): The fan blade is sheared off and jammed into the condenser coil.  This happened during power transfer from generator power to commercial power.  Naturally, it was at 1 am in the morning after a pole mounted transformer had been replaced.  When the building transfered back to commercial power, I went outside to use the “bathroom” before my two hour drive back home.  I though I smelled something hot, you know that cooked paint/plastic smell, but couldn’t really track it down… the winds were kicking up and another thunderstorm was on the way. The next afternoon, however, when the sun was up and the site was working on one air conditioner, the temperature alarm went off.  Upon arrival, I found the condenser breaker tripped, resetting it caused the building lights to dim.  The fan motor was shorted to case.  I would theorize the aluminum fan blade suffered from metal fatigue, likely because the blades were not balanced causing a vibration.  

When the power transfer occurred, there was just the right combination of torque and centripetal force to cause the blade to rip, then lodge in the condenser coil. The fan motor has replaced, but I think it is time to replace the whole condenser unit, which will be expensive. I found having a set of gauges to check the head pressure and suction is a good diagnostic tool to quickly pinpoint problems with HVAC units.  This way, when the HVAC tech shows up, you can quickly point him in the right direction.Alternating Current Systems Overview: Water to wire.... how the electricity is generated. (See below for hydro definitions) The following text explains the key components in a typical installation. The process begins with the water in the creek having a potential energy equal to its mass times its height above the turbine mounted on the power house floor. The water is slowed in a pool so the sand can settle out. Larger debris is also filtered out here. Excess water passes over a low weir, or barrier, with a controlled amount entering a large pipeline or 'penstock'.

Water flows down the pipe at a slow rate of speed, typically 5 feet per second. The pressure steadily increases in proportion to the increasing drop. It is the high pressure that forces the water out the nozzle. The actual rate of flow in the penstock is relatively unimportant, unless the pipe is very long in which case an excessive amount of friction is created by the flowing water. This is the heart of the energy conversion process which changes the waters velocity into mechanical energy. Water striking the curved blades of the turbine imparts its kinetic energy of motion on the blades. The turbine spins at slightly less than one half the jet velocity, and falls away from the turbine with virtually zero energy. Manual control of the power produced can be made by adjusting the amount of water passing through the turbine. This is accomplished by adjusting a threaded spear which screws into the nozzle assembly where the penstock enters the turbine. This pinches off the flow in any amount required.

Typically, the control is set to the maximum power required, and the governor then maintains control by dumping any excess power. Within the generator there are many coils of wire wound on iron cores attached to the generator frame. Rotating inside these coils is an iron core which produces strong magnetic fields. As the core rotates at 1800 revolutions per minute, the magnetic lines of force pass through the fixed windings. It is this process that produces the alternating current electricity. This same principle is used in all electric generators, from large hydro and nuclear plants to the alternator in your car, although the speed can vary depending on the type of generator used. This is the main controller for the entire system. Precise powerline frequency is controlled by keeping an exact amount of load on the generator. This load must exactly balance the energy being delivered to the turbine. This is accomplished by rapidly switching on and off ballast loads in a water filled load tank.

A second function of the governor panel is to report all the conditions of the system, and any alarms that may result from improper operation. In the rare event of a system alarm, the governor will immediately shut the whole system down by activating a jet deflector which diverts the water jets away from the turbine. This is generally made up of a large water tank, or series of separate tanks containing electric heating elements. Excess power is shunted to these elements from the governor thereby "putting the brakes on" the generator. This excess power is often used to heat primary domestic hot water in smaller, separate water tanks, one large central tank, or as a low priority source of heat for a pool or sauna. As lights are turned off in the buildings, the power is immediately directed to the ballast load to maintain the exact balance necessary for precise frequency control. Over the course of the night, large amounts of hot water can be produced and stored for use during the day.

This method of frequency control maximizes the hydro plant capacity and reduces or eliminates the need for fossil fuel boilers. The secret to how a 200 kW hydro plant can provide power to a total load of 300 kW or more. In addition to the governor controlling the precise speed of the generator and hence line frequency, load management diverts available power to useful loads arranged in a pritorized sequence. The load manager is always testing the power being dumped in the ballest load and when there is sufficient excess, another prioritized load turns on. These consist of water tanks, space heaters, display lighting, dryers, freezers, or any other load that can be shut off for a period of time with no ill effect. Base loads such as lighting, pumps, outlets, kitchen appliances, sound equipment, computers, communications etc. are always connected. A load center is basically a large switch with up to 24 smaller switches serving as circuit breakers. These will protect the wires and equipment from potential short circuits or overloads.

You will have a similar 'electrical panel' in your home. Each building has a load center, and each load center will supply power to all the branch circuits in that building. Definitions used with Micro Hydro Here is an (incomplete) list of common terms and their explanation. The total available drop from intake to turbine nozzle. The useable head after subtracting losses from pipe friction etc. The quantity of water being used to produce power. this is usually measured in units of cubic feet per second, gallons or liters per second. The rate of doing work, or energy expended per unit of time. Often used inter-changeably, thought not technically correct, with energy. The ability to do work, energy can be potential as in water behind a dam being acted upon by gravity. Energy can also be kinetic, that is, the combination of mass times velocity, as in moving water in a penstock. One thousand watts - Joules etc The units of electrical pressure and quantity