Boots – shoes – and leggings
Patent
1996-07-19
1998-08-18
Trammell, James P.
Boots, shoes, and leggings
364572, 364480, 364481, 364483, 361160, 361187, H02J 1300
Patent
active
057966303
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a protective relay system provided with a difference filter and an addition filter, and more particularly to a protective relay system substantially free from influence of harmonic components which may be included in a fault current.
Background Art
The main technical object of protective relay systems used for protecting the power system is to lessen influence of harmonic components of fault current and fault voltage produced at the time of system failure. Particularly, in recent years, since charge capacity component of the system in equipments or facilities such as cable (power) transmission line and/or phase modifying capacitor, etc. has been increased, the order of harmonic wave produced in the system power has tendency to increase (value twice or three times greater than the fundamental wave).
For this reason, in a method of attenuating harmonic components by filter which has been conventionally applied, it is necessary to prolong delay time of the filter in order to ensure desired attenuation quantity, resulting in delayed operation time of the relay. In order to solve such a problem, there has been conventionally employed an approximation system such that even if any harmonic component is included in the system power, there essentially results no influence of the harmonic wave.
One example of the system employed at present will be described below.
In a transmission line 2 of FIG. 1, assuming now that voltage and current at point A of installation of a protective relay 1 are respectively v and i when transmission line impedance constants up to the fault point F are such that resistance is R and inductance is L, the differential equation of the transmission line 2 is expressed by the following equation (1) in the case where fault point (F) voltage is zero. By carrying out approximate calculation of the differential term (di/dt) of this equation (1), it is possible to calculate, with high accuracy, value proportional to inductance L without eliminating harmonic wave by using filter. ##EQU1##
An example of an actual method for digital operation practically applied is indicated below. -i.sub.m-1) v.sub.m-1 +v.sub.m-2 =R.multidot.(i.sub.m-1 +v.sub.m-2)+L.multidot.(i.sub.m-1 -V.sub.m-2) (2)
When X(=.omega..sub.0 .multidot.L) is calculated from the equation (2), the following equation (3) is obtained. The frequency characteristic of the reactance value X.sub.m /X (true value) is represented by the following equation (4), and its characteristic is as indicated by line (a) of FIG. 2. FIG. 2 is a graph in which frequency is taken on the abscissa and reactance measured value is taken on the ordinate. In this case, the line (a) indicates the characteristic in the case where sampling frequency is 600 Hz, and the line (b) indicates the characteristic in the case where sampling frequency is 4800 Hz. ##EQU2##
In this case, since i.sub.m =I.multidot.sin (.omega.t.sub.m) and v.sub.m =V.multidot.sin (.omega.t.sub.m +.theta.), differential approximation quantity "i.sub.m -i.sub.m-1 " and diffentiated quantity "v.sub.v +v.sub.m-1 " can be respectively expressed by the following equations (5) and (6). (.omega.T/2).multidot.cos(.omega.t.sub.m -.omega.T/2) (5) -.omega.T/2+.theta.) (6)
In the above equation, T is sampling period, .omega. is angular frequency, and .theta. is voltage lead phase with respect to current.
As shown in FIG. 2, it is understood that according as frequency deviates from that of the fundamental wave, value of L.sub.m /L (true value) becomes smaller than 1. This value is permitted to keep value in the vicinity of 1 at values approximately twice or third times greater than the fundamental wave if the value of (.omega.T/2) is further held down to lower value (the sampling period is reduced). The frequency characteristic when the sampling frequency is set to value eight times greater than the fundamental wave is shown FIG. 2(b). Namely, from a qualitative point of view, the relationship between the differential approximation quantity "i.sub.m -i.sub.m-1 " and
REFERENCES:
patent: 5455776 (1995-10-01), Novosel
patent: 5506789 (1996-04-01), Russell et al.
patent: 5523675 (1996-06-01), Kurosawa
patent: 5572138 (1996-11-01), Nimmersjo 364483
Andow Fumio
Kurosawa Yasuhiro
Maeda Takafumi
Yamakawa Hiroshi
Yamaura Mitsuru
Kabushiki Kaisha Toshiba
Trammell James P.
Wachsman Hal D.
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