The Klydonograph to the measurement of voltages-surge on transmission lines. klydonograph is placed directly on the line.
Klydonograph is a device which makes use of patterns known as Lichtenberg Figure Which are produced on photographic in by surface corona discharge. Since lighting surge is infrequent and random in nature. Hence it is necessary to install a large no. of recording devices to obtain a reasonable amount of date regarding these surges produced on transmission lines and other equipment.
Klydonograph consists of around electrode resting on the emulsion side of photographic plates as shown in Figure (2.25)
The homogenous insulating plate is placed between the photographic plate and a metal plate electrode. This insulating plate has a smooth surface. When an electric held is applied between the electrode, the photographic plate is affected and figure known as “Lichtenberg Figure” are produced. The minimum critical voltage required to produce such a figure is 2kV and the maximum voltage that can be recorded is 18kV because at higher voltage spark-over occurs and fogs the film.
The shape and configuration of the figure are functions of the wave shape of the impressed voltage while the radius of Lichtenberg Figure produced is a function of the crest of the impressed voltage. From the shape and size of the figure, an estimate regarding the magnitude, wavefront, and polarity of the wave can be made.
The Klydonograph to the measurement of voltages on transmission lines, either a capacitance PD. is used or the hook On type klydonograph is used which is placed directly on the line.
Hook on type klydonograph consists of:
(a) Recording unit
(b) Coupling hood
(c) Sensitivity rod
(d) Supporting hook
This figure (2.26) shows the details of various parts.
(a) Recording unit:
The recording unit houses the photographic film in a light-proof chamber. The unit consists of two bakelite cups which can be screwed on. Circular bakelite plate is placed between the cups on each side of which the photographic film is placed with the emulsion facing out. The bakelite cups are coated with conducting paint in their inner surface to provide a well defined electric field which increases the accuracy of the measurement.
(b) Coupling hood:
The coupling hood provides for voltage division of the surge to the ground at the h.v. end. Due to the capacitance between the hood and sensitivity rod, a small portion of the surge voltage appears across the conducting layers on the bakelite cups.
(c) Sensitivity rod:
A metallic cylindrical rod screwed to the bottom bakelite cup. Length of this rod controls the magnitude of the voltage across the klydonograph.
(d) Supporting hook:
The supporting hook supports the hood and the recording unit and connects them to the high voltage conductor.
It is a relatively simple and cheap instrument and has been very useful for determining data regarding magnitude, polarity, and frequency of voltage surge on the transmission line. Its accuracy is of the order of 25% to 50%.