Conventional air brakes require a reduction in brake pipe pressure by the driver's brake valve, which must be propogated to all the vehicles of the train. The air exhausts from the brake pipe through a port in the driver's valve, which means vehicles towards the front of the train brake sooner than towards the rear, which makes for tricky train handling on long trains.
With EP braking (used on fixed length trains like EMU's, DMU's) electric circuits are energised through the entire train length (typically via the jumper connections), resulting in the air brakes being released. When the driver applies the brake the electric circuits are de-energised in sequence, causing activation of the brake equipment on each vehicle at the same time, resulting in reduced or no 'run-in' and carriage jostle.
Red Rattlers had a single step EP, the electric feed passing from the drivers brake valve then (via a special jumper coupling) to every carriage in the set, to a terminating plug at the end of the last carriage. The brake handle would be moved towards the application position, the bakes on each car would start to apply; when sufficient braking effort had been attained, by moving the brake handle back towards release, the EP wire would energise again and keep the brake effort at that level.
Newer trains have three (or more?) wires, all energised when the brake handle is in release. As the brake handle is moved towards full application, switches in the driver's brake unit open and close in a binary sequence, and does not need to be moved back towards release to set a partial application of the brakes.
100 Half brake effort
000 Emergency (The train separating has the same effect)
I could guarentee all suburban rolling stock (Tangaras onward) would have some form of EP brake.
I know of no locomotives in Australia having support for EP brake, since freight trains are longer than the electric circuits would allow, but locomotive-hauled passenger trains (like RUB sets and I-P style cars that already had electrical jumpers between cars) would have benefited from EP, and I've read of at least one U.S. steam locomotive class having it.
Long freight trains that utilise mid-train or rear locomotives (or via a control truck such as Locotrol), can initiate a brake pipe reduction on the remote locomotives (as noted in the following message by KRviator) when the driver (on the lead loco) operates his brake valve; this speeds up activation of brakes from the rear of the train and helps to minimise 'run-in' . This isn't really a form of EP since it only allows brake pipe reductions on the locomotives of the train, but it does provide similar benefit and trains of 1.5 km possible with a single crew.
Electric forms of braking have locomotive or train traction motors switched to function as generators, being driven by the forward movement of the train. As already noted here, this means that at low speeds or standstill there is no braking force, and hence it cannot hold a train on a grade.
Diesel-electric locomotives are usually fitted with dynamic brake. In this form the electical energy generated by the traction motors is disipated in on-board resistor banks cooled by a (usually noisy) electrically-driven fan. The driver can control the amount of power generated, but once the maximum power is reached, control systems automatically ensure the maximum is not exceeded, regardless of how fast the train goes.
Electric locomotives and EMU's can optionally have regenerative brake or possibly synchronous braking.
In regenerative braking, power generated by the traction motors is supplied back to the overhead wire, and could be used by other electric trains in the same section. If there were no electric trains in the section the power was disipated in large resistor banks at the sub-stations.
The original single-deck interurbans (and possibly the double-deckers) had a 'blended' brake system such that if the driver applied the brakes at high speed, regenerative braking would commence first, then, as the train slowed to the point where regenerative braking was less effective, it would switch off automatically and allow the conventional EP air braking system to bring the train to a stand.
46/85/86 class locomotives had regenerative braking selected and controlled solely by the driver.
I never worked on or saw circuit diagrams for Tangaras or later so cannot say if any of them support(ed) regenerative brake. From what I've noticed in recent years, the resistor banks in substations have been removed, which suggests regenerative braking may have been phased out altogether. Someone who knows is welcome to comment on this point.
Regardless of wether brakes are activated be brake pipe reduction or EP, air is made available to one or more pistons to push brake shoes on to friction surfaces that absorb the forward energy of the train.
Clasp brakes press brake shoes onto the wheel tread of each wheel, two shoes per wheel. The brake shoes in this configuration kept the wheel surface free of scale, which is useful for electric trains and EMS's that need to get electric current back to the substation. If a wheel locked up under high braking it could produce a small flat spot on the wheel tyre face. Cast iron brake shoes could be sometimes used to wear off these small flats, obviating need for wheel turning.
Disc brakes have the advantages of larger brake surface and likely ease of access for maintenance, and does not cause heating of the wheel rims under high-speed braking, resulting in better wheel life.