KOLEN – founded in 1992 – specializes in issues concerning fault to earth and electric shock protection and stray current limitation in the vicinity of DC traction system. All manufactured products, specialized measuring instruments and test apparatuses were entirely invented and designed (starting from guidelines to the final product) by the company and employed solutions are patented. The low-voltage TZD limiters are basic products. Depending on the type limiters can be used in the bonding (connecting with running rails) of railway support structures or other individual object requiring bonding due to the earth fault protection. Limiters guarantee required level of the ground protection and they limit significantly stray currents. They can also be used in return wires of MV cables to limit stray currents. The overvoltage limiters TOP are designed to be installed parallel to the choking coil in substations. Apart from limiting overvoltages they reduce (several times) the arc energy released in the HSB arc chute during short-circuit and overloading switching off. To test the low-voltage limiters correct work the special test apparatus TOZ is manufactured. It can check the limiter on site without deenergizing OCL. The TCK tester is designed for the check of earthing and bonding continuity what has an impact on assurance of the ground breaking capacity. The tester can also monitor the earth electrode resistance of the substation/sectioning cabin. The resistance impulse meter IMR is a unique device to take earth electrode (single or compound) resistance measurements using running rails (constituting the return circuit of DC railway system) as a reference probe. The meter can also be used in potential method of the earth electrode resistance measurements (using compound earth electrode of supply system or voltage and current probes). Now the meter is adapting to the touch voltage measurement in transformer stations. Recently KOLEN launched a new product on – the TWS test apparatus family for high speed breakers (HSB) diagnostic tests. TWS testers measure: current adjustment up to 6000A, breaking time, closing-on capability, main contact resistance. As a current injection there is a battery of ultracapacitors with connection of controlled resistance. TWS needs one-phase line 230V/50Hz supply and maximal power consumption is not more then 2 kVA. The tester weight is about 50 kg.