The paper analyzes the known methods of measuring synchronous generator time constants based on field quenching experiments. It shows that these methods are difficult to implement under the operating conditions of a power station generator. The paper further subatantiates the possibility of using methods that maximize the use of standard equipment and elements of the generator system circuits, in particular, a DC circuit with a winding and excitation system. These methods are as follows: the removal of control pulses from the thyristors of the exciter transducer; using standard protection against the closures on contact rings; additional shunt diode usage. The verified comparative results of experiments performed by different methods are given. The considered experiments are applicable to the implementation of all known DC decay test methods in the presence of a DC source independent of the tested generator (independent excitation system of a neighboring generator, backup excitation system or excitation system powered by the power plant's own needs).