The Klydonograph to the measurement of voltages-surge on transmission lines. Klydonograph is placed directly on the line.
- From the shape and size of the figure, an estimate regarding the magnitude, wavefront, and polarity of the wave can be made.
- It 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 ( rare ) and random in nature.
- Hence it is necessary to install a large no. of recording devices to obtain a reasonable amount of data regarding these surges produced on transmission lines and other equipment
It Is consists of around electrode resting on the emulsion side of photographic plates. Klydonograph Diagram 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.
- Thus it’s possible to understand whether the wave is unidirectional or oscillatory.
- Since the dimensions of the Figure for positive polarity is larger, it’s desirable to use a positive polarity Figure.
- This can be particularly desirable just in case of mensuration of surges on transmission lines or different such instrumentality which are commonly operative on a.c. voltage and also the alternating voltage provides a black band in the middle of the film caused by the superposition of positive and negative Figure made on every half-cycle.
- For each surge voltage, it’s possible to get both positive and negative polarity Figure by connecting pairs of electrodes in parallel, one pair with a high voltage point and an earthed plate and also the different try with a high voltage plate and an earthed point.
- 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.
- The Klydonograph to the measurement of voltages on transmission lines, either a capacitance PD is used which is placed directly on the line.
It has been used in the past quite extensively for providing statistical data on the magnitude, polarity, and frequency of voltage surges on transmission lines even though its accuracy of measurement is only of the order of 25 percent.
Construction Of Surge Recorder
(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%.