JP2728486B2 - Power limiting protection relay - Google Patents
Power limiting protection relayInfo
- Publication number
- JP2728486B2 JP2728486B2 JP1024631A JP2463189A JP2728486B2 JP 2728486 B2 JP2728486 B2 JP 2728486B2 JP 1024631 A JP1024631 A JP 1024631A JP 2463189 A JP2463189 A JP 2463189A JP 2728486 B2 JP2728486 B2 JP 2728486B2
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- JP
- Japan
- Prior art keywords
- power
- frequency
- detection relay
- relay
- deviation
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Description
【発明の詳細な説明】 〔産業上の利用分野〕 本発明は、電力系統において負荷脱落などが生じた際
に発生する周波数の上昇現象に対して系統及び機器保護
を確立する火力発電機の電源制限用保護継電器に関する
ものである。DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a power supply for a thermal power generator that establishes protection of a system and equipment against a frequency increase phenomenon that occurs when a load drop or the like occurs in a power system. It relates to a protection relay for restriction.
従来、この種の負荷脱落に伴う周波数上昇時の系統及
び機器保護に関しては情報伝送装置を使用し各系統から
の情報を入力源として系統の安定化を図る各種系統安定
化装置又は自端の周波数情報のみを使用したOver Frequ
ency Relay（周波数上昇防止リレーで、以下OFRと称
す）などが使用されている。前者は、その装置構成の要
素として情報伝送装置を必要とするため、装置構成が大
規模となり装置の信頼度確保が問題であった。このた
め、自端情報のみで処置が可能なOFRが見直される状況
にある。第３図（ａ），（ｂ）はモデル系統における事
故前及び事故後の系統を想定した図である。次に第３図
（ｂ）の動作について説明する。まず発電機PG1〜PG3の
慣性定数をMi（ｉ＝1,2,3）、周波数をfi（ｉ＝1,2,3）
とすると、ガバナ等の発電機制御が実施されない時には
各発電機PG1〜PG3の周波数fiは下記の運動方程式より算
出できる。すなわち ここでPGf:発電機出力、PL1〜PL3:負荷である。Conventionally, with regard to protection of the system and equipment when the frequency rises due to this type of load drop, various system stabilization devices that use an information transmission device and stabilize the system using information from each system as an input source, or the frequency at the local end Over Frequ using information only
ency Relay (frequency rise prevention relay, hereinafter referred to as OFR) is used. The former requires an information transmission device as an element of the device configuration, so that the device configuration becomes large-scale, and there is a problem in securing the reliability of the device. For this reason, there is a situation in which OFRs that can be treated only by own-end information are reviewed. FIGS. 3A and 3B are diagrams assuming a system before and after the accident in the model system. Next, the operation of FIG. 3 (b) will be described. First, the inertia constants of the generators P G1 to P G3 are Mi (i = 1, 2, 3), and the frequency is fi (i = 1, 2, 3).
When, when the generator control of the governor and the like is not performed frequency fi of each generator P G1 to P G3 can be calculated from equations of motion for the following. Ie Here, P Gf is a generator output, and P L1 to P L3 are loads.
しかし、実際の系統ではガバナ制御などにより発電機
への機械入力をしぼり発電機出力PGiを減少させて周波
数fiの上昇を防止するような制御方法が実施される。従
って、このガバナ制御などで、たとえ周波数の上昇が防
止できたとしても、ボイラー系の制御とは全く無関係に
実施されるためにボイラー系に蒸気圧の上昇に伴うスト
レスが与えられる。このストレスkpiは、ほぼ（４）式
で示される。However, in an actual system, a control method is performed in which a mechanical input to the generator is squeezed by governor control or the like to reduce the generator output P Gi to prevent an increase in frequency fi. Therefore, even if the rise of the frequency can be prevented by the governor control or the like, since the boiler system is implemented completely independently of the control of the boiler system, the boiler system is given a stress due to the increase of the steam pressure. This stress k pi is substantially expressed by equation (4).
ここで、PL3fとは負荷PL3が脱落した時のｉ番目の発
電機の負荷の変動量で、このストレスkpiがある値より
大きくなると、ボイラーの蒸気圧の上昇値やボイラー水
冷壁の温度上昇値が許容限界値を越えることになるた
め、MFT（Master Fuel Tripの略称で、主燃料しゃ断の
意）トリップに至り全発電機が脱落するなどの可能性が
ある。 Here, P L3f is the amount of change in the load of the i-th generator when the load P L3 falls off. When this stress k pi becomes larger than a certain value, the boiler steam pressure rise value and the boiler water cooling wall Since the temperature rise exceeds the allowable limit, there is a possibility that the MFT (Master Fuel Trip, short for main fuel cut-off) trip will occur and all generators will fall off.
従来の電源制限用保護継電器は以上のように構成され
ていたので、例えば負荷PL3の脱落に対しては適切な制
御を施すことにより負荷PL3に相当する発電機、例えばP
G3の系統よりの解列で系統の安定化を図ることが可能で
ある。しかし、OFRが第４図のような動作特性であるた
めに、適切な制御がなされない場合には発電機自身が機
器保護のために独自の判断で系統より脱落してしまい、
この場合には、無制御状態となり、発電機PGi（ｉ＝1,
3）全てが脱落し系統が全停止するということも起りう
るなどの問題点があった。Since the conventional power limiting protection relay has been configured as described above, for example, a generator which correspond to the load P L3 by performing appropriate control for shedding load P L3, for example, P
It is possible to stabilize the system by disconnecting from the G3 system. However, if the OFR has the operating characteristics as shown in Fig. 4 and proper control is not performed, the generator itself will fall out of the system at its own discretion to protect the equipment.
In this case, a non-control state is established, and the generator P Gi (i = 1,
3) There was a problem that it was possible that all of the systems were dropped and the system was completely shut down.
本発明は上記のような問題点を解消するためになされ
たもので、周波数の上昇並びに有効電力の変化に対して
も応動するようにした電源制限用保護継電器を得ること
を目的とする。SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a protection relay for limiting power supply that can respond to a rise in frequency and a change in active power.
この発明に係る電源制限用保護継電器は、電力偏差検
出リレー及び周波数偏差検出リレーの少なくとも一方か
ら動作信号を出力されると、発電機をトリップするトリ
ップ信号を出力するようにしたものである。The power limiting protection relay according to the present invention outputs a trip signal for tripping the generator when an operation signal is output from at least one of the power deviation detection relay and the frequency deviation detection relay.
〔作用〕 この発明における電源制限用保護継電器は、電力偏差
検出リレー及び周波数偏差検出リレーの少なくとも一方
から動作信号を出力されると、発電機をトリップするト
リップ信号を出力するOR回路を設けたことにより、周波
数が大きく上昇した場合に限らず、有効電力の偏差が大
きく変動した場合にも発電機を停止できるようになる。[Operation] The power limiting protection relay according to the present invention includes an OR circuit that outputs a trip signal that trips the generator when an operation signal is output from at least one of the power deviation detection relay and the frequency deviation detection relay. Accordingly, the generator can be stopped not only when the frequency rises significantly but also when the deviation of the active power greatly fluctuates.
以下、本発明の一実施例を図について説明する。今、
事故後の状態、すなわち第３図（ｂ）におけるように負
荷PL3が脱落すると発電機PGi（ｉ＝１〜３）の電気的出
力が減少し、これに起因して、発電量が負荷量より大き
くなるため、周波数は上昇する。この時の現象は、第２
図における点（Ｏ）から点（Ａ）への周波数偏差Δｆ及
び有効電力の偏差ΔＰとなる。周波数が上昇すると、タ
ービンのガバナ制御などにより発電機への機械入力をし
ぼる為に周波数は低下しはじめる。この状態が点（Ａ）
から点（Ｂ）への変化である。しかし点（Ｂ）の状態で
は周波数がまだ規定値を越えているのでOFR要素は動作
をする。この時には、発電機の一部がしゃ断されるため
有効電力偏差ΔＰも周波数偏差Δｆも減少する。第２図
の点（Ｂ）から点（Ｃ）への動きに相当する。すなわち
従来のOFRの動作は点（Ｃ）までである。しかし、この
状態は、ガバナ動作による制御分だけの有効電力偏差Δ
Ｐがボイラー系にストレスをかけた状態であり、第２図
の点（Ｃ）はその有効電力偏差値ΔＰが規定値P0を越え
ている事をしめしている。この為、ある時間以上経過す
ると蒸気圧力などが上昇してくる。この為ボイラー系保
護を目的とし発電機は例えばMFTトリップとなり需給バ
ランスからみると無制御な状態で発電機は系統から解列
される。これを防止する為には、有効電力偏差ΔＰを検
出し、その偏差値が規定値ΔP0を一定時間以上越えれば
発電機を解列する制御、すなわち第２図の点（Ｃ）から
点（Ｄ）への制御を実施すればよい。Hereinafter, an embodiment of the present invention will be described with reference to the drawings. now,
When the load PL3 falls off after the accident, that is, as shown in FIG. 3 (b), the electric output of the generator P Gi (i = 1 to 3) decreases, and as a result, the power generation amount decreases. Because it is larger than the amount, the frequency increases. The phenomenon at this time is the second
The frequency deviation Δf from the point (O) to the point (A) in FIG. When the frequency increases, the frequency starts to decrease because the mechanical input to the generator is squeezed by governor control of the turbine or the like. This state is point (A)
From the point (B) to the point (B). However, in the state of point (B), the OFR element operates because the frequency is still beyond the specified value. At this time, since a part of the generator is cut off, both the active power deviation ΔP and the frequency deviation Δf decrease. This corresponds to the movement from point (B) to point (C) in FIG. That is, the operation of the conventional OFR is up to the point (C). However, this state is due to the active power deviation Δ only for the control by the governor operation.
P is a state where stress is applied to the boiler system, and point (C) in FIG. 2 indicates that the active power deviation value ΔP exceeds the specified value P 0 . For this reason, the vapor pressure or the like increases after a certain period of time. For this reason, for the purpose of boiler system protection, the generator becomes an MFT trip, for example, and the generator is disconnected from the grid in an uncontrolled state in view of supply and demand balance. In order to prevent this, detects the effective power difference [Delta] P, the deviation is the specified value [Delta] P 0 for a predetermined time or more exceeds if the generator control for disconnection, i.e. the point from the point of FIG. 2 (C) ( What is necessary is just to implement control to D).
ここで、有効電力偏差ΔＰとは、事故前の発電機の出
力と事故後の発電機の出力との差であり、この差の値に
より事故前後の発電プラント全体のストレスを測定する
ことができる。Here, the active power deviation ΔP is a difference between the output of the generator before the accident and the output of the generator after the accident, and the stress of the entire power plant before and after the accident can be measured by the value of the difference. .
第１図は、本発明の具体例を示す電源制限用保護継電
器の回路構成例で、図は主保護要素のみを記述しており
実際に実施するには、例えば不足電圧継電器の様なフエ
イル・セイフ要素が別に設置される。FIG. 1 is a circuit configuration example of a power limiting protection relay showing a specific example of the present invention. FIG. 1 shows only a main protection element. Safe element is installed separately.
まず、図において、１は電力偏差検出リレーで、発電
機出力の電流Ｉと電圧Ｖとの瞬時値より、有効電力を演
算する。例えば、電源制限用保護継電器が設置されてい
る発電所の電圧Ｖと電流Ｉとの瞬時値を計測し、有効電
力を演算しており、これは電力系統の電圧及び電流を計
測していることに相当する。11は有効電力検出要素、12
は前記有効電力検出要素11の時々刻々の瞬時値をある一
定時間記憶する記憶要素、13は有効電力の変化分検出要
素、15は基準値設定要素、14は前記規準値設定要素15の
出力と実際の電力検出値とを比較し動作又は不動作を判
定する判定要素、16はタイマーである。また、２は周波
数偏差検出リレーで、これは系統周波数（例えば、電源
制限用保護継電器が設置されている発電所の電力系統の
電圧の瞬時値より計測される。）の検出要素21、規準値
設定要素25、規準値と実際の周波数検出値とを比較し、
動作又は不動作を判定する判定要素24及びタイマ26とを
備えている。また３は電力偏差検出リレー１及び周波数
偏差検出リレー２の少なくとも一方から動作信号を出力
されると、発電機をトリップするトリップ信号を出力す
るOR回路である。First, in the drawing, reference numeral 1 denotes a power deviation detection relay, which calculates active power from an instantaneous value of a current I and a voltage V of a generator output. For example, the instantaneous value of the voltage V and the current I of the power plant where the protective relay for limiting the power supply is installed is measured, and the active power is calculated, which measures the voltage and the current of the power system. Is equivalent to 11 is the active power detection element, 12
Is a storage element that stores the instantaneous value of the active power detecting element 11 every moment for a certain period of time, 13 is an active power change detecting element, 15 is a reference value setting element, and 14 is an output of the reference value setting element 15. A determination element 16 for comparing the actual power detection value with the actual power detection value to determine operation or non-operation is a timer. Reference numeral 2 denotes a frequency deviation detection relay, which detects a system frequency (for example, measured from the instantaneous value of the voltage of the power system of the power plant in which the power supply limiting protection relay is installed), and a reference value. Setting element 25, comparing the reference value with the actual frequency detection value,
It includes a determination element 24 for determining operation or non-operation and a timer 26. An OR circuit 3 outputs a trip signal for tripping the generator when an operation signal is output from at least one of the power deviation detection relay 1 and the frequency deviation detection relay 2.
次に第１図の動作について説明する。まず、電力偏差
検出リレー１の具体的な演算動作は下記の通りである。
ある時刻の電流と電圧をｖ（ｔ）,i（ｔ）とすると有効
電力検出要素11は前記ｖ（ｔ）とｉ（ｔ）より有効電力
ｐ（ｔ）を算出する。そこで記憶要素12は時々刻々変化
する有効電力ｐ（ｔ）をある時間（tn）だけ記憶し、有
効電力ｐ（ｔ−tn）を出力する。そこで有効電力の変化
分検出要素13では有効電力偏差ΔＰ（ｔ）＝ｐ（ｔ）−
ｐ（ｔ−tn）の演算を実行する事により有効電力偏差Δ
Ｐ（ｔ）を算出し、この値と有効電力偏差の規定値（Δ
P0）との比較演算、ΔＰ＝ΔＰ（ｔ）−ΔP0を判定要素
14で実施する。前記判定要素14における比較演算ΔＰが
正の時間で、タイマー16が設定時間以上継続すると電力
偏差検出リレー１は動作信号を出力する。周波数偏差検
出リレー２も上述と同様の動作で略作動するが周波数偏
差Δｆは規定値Δf0からのずれでよいため前記電力偏差
検出リレー１の記憶要素12及び有効電力の変化分検出要
素13に相当する構成が省略された構成となる。Next, the operation of FIG. 1 will be described. First, a specific calculation operation of the power deviation detection relay 1 is as follows.
Assuming that the current and the voltage at a certain time are v (t) and i (t), the active power detection element 11 calculates the active power p (t) from the v (t) and i (t). Thus, the storage element 12 stores the constantly changing active power p (t) for a certain time (tn) and outputs the active power p (t−tn). Therefore, in the active power change detecting element 13, the active power deviation ΔP (t) = p (t) −
By executing the calculation of p (t−tn), the active power deviation Δ
P (t) is calculated, and this value and a specified value (Δ
P 0 ), and ΔP = ΔP (t) −ΔP 0
Perform at 14. When the comparison operation ΔP in the determination element 14 is a positive time and the timer 16 continues for a set time or more, the power deviation detection relay 1 outputs an operation signal. The frequency deviation detection relay 2 also operates substantially in the same manner as described above, but the frequency deviation Δf may be a deviation from the specified value Δf 0 , so that the storage element 12 and the active power change detection element 13 of the power deviation detection relay 1 are used. The corresponding configuration is omitted.
尚、電力偏差検出リレー１及び周波数偏差検出リレー
２のタイマ16及び26の設定値は当然時間協調を取る必要
がある。この時間協調は第２図のようにまず周波数偏差
検出リレー２が動作し次に電力偏差検出リレー１が動作
する。Incidentally, the set values of the timers 16 and 26 of the power deviation detection relay 1 and the frequency deviation detection relay 2 must naturally cooperate with each other. In this time coordination, first, the frequency deviation detection relay 2 operates, and then the power deviation detection relay 1 operates, as shown in FIG.
実際の適用にあたっては電力偏差検出リレー１及び周
波数偏差検出リレー２はタイマー時間を複数組設定した
設定器を組合せて適用する。In actual application, the power deviation detection relay 1 and the frequency deviation detection relay 2 are applied in combination with a setter in which a plurality of sets of timer times are set.
この場合、周波数偏差検出リレーの動作タイマー値よ
り電力偏差検出リレーの動作タイマー値の方を長く設定
する。In this case, the operation timer value of the power deviation detection relay is set longer than the operation timer value of the frequency deviation detection relay.
なお、本発明の電源制限用保護継電器は、複数の発電
機から構成される発電所に設置されることを前提として
おり、周波数偏差検出リレーによるトリップ信号が出力
された後に、電力偏差検出リレーの動作信号が出力され
た場合には、それぞれ別の発電機がトリップされ、既に
解列した発電機に再度トリップ信号が送られることはな
い。Note that the power limiting protection relay of the present invention is supposed to be installed in a power station composed of a plurality of generators, and after the trip signal is output by the frequency deviation detection relay, the power deviation detection relay When the operation signal is output, another generator is tripped, and the trip signal is not sent again to the already disconnected generator.
以上のように、この発明によれば、電力偏差検出リレ
ー及び周波数偏差検出リレーの少なくとも一方から動作
信号を出力されると、発電機をトリップするトリップ信
号を出力するように構成したので、周波数が大きく上昇
した場合に限らず、有効電力の偏差が大きく変動した場
合にも発電機を停止できるようになり、その結果、蒸気
圧の上昇に伴うボイラー系へのストレスを抑制できるな
どの効果がある。As described above, according to the present invention, when an operation signal is output from at least one of the power deviation detection relay and the frequency deviation detection relay, a trip signal for tripping the generator is output. The generator can be stopped not only when it rises significantly but also when the deviation of the active power fluctuates greatly. As a result, it is possible to suppress the stress on the boiler system due to the rise in steam pressure. .
第１図は本発明の一実施例による電源制限用保護継電器
の要素構成図、第２図は本発明の一実施例による電源制
限用保護継電器の動作特性図、第３図は本発明を説明す
るための電力系のモデル系統図、第４図は従来の電源制
限用保護継電器の動作特性図である。 １は電力偏差検出リレー、２は周波数偏差検出リレー、
３はOR回路、11は有効電力検出要素、12は記憶要素、13
は有効電力の変化分検出要素、14は判定要素、15は基準
値設定要素、16,26はタイマー、21は系統周波数の検出
要素、24は判定要素、25は基準値設定要素。 なお、図中、同一符号は同一部分を示す。FIG. 1 is an element configuration diagram of a power limiting protective relay according to an embodiment of the present invention, FIG. 2 is an operation characteristic diagram of the power limiting protective relay according to an embodiment of the present invention, and FIG. 3 explains the present invention. FIG. 4 is a diagram showing operation characteristics of a conventional power supply limiting protective relay. 1 is a power deviation detection relay, 2 is a frequency deviation detection relay,
3 is an OR circuit, 11 is an active power detection element, 12 is a storage element, 13
Is a change detection element of active power, 14 is a judgment element, 15 is a reference value setting element, 16 and 26 are timers, 21 is a system frequency detection element, 24 is a judgment element, and 25 is a reference value setting element. In the drawings, the same reference numerals indicate the same parts.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 合田 忠弘 兵庫県神戸市兵庫区和田崎町１丁目１番 ２号 三菱電機株式会社制御製作所内 (72)発明者 成田 利春 兵庫県神戸市兵庫区和田崎町１丁目１番 ２号 三菱電機株式会社制御製作所内 (72)発明者 松沢 邦夫 山梨県甲府市丸の内１丁目10番７号 東 京電力株式会社山梨支店内 (72)発明者 笠原 利夫 栃木県宇都宮市馬場通り１丁目１番11号 東京電力株式会社栃木支店内 (56)参考文献 特開 昭64−1430（ＪＰ，Ａ) 特開 昭55−147923（ＪＰ，Ａ) 特開 昭63−11025（ＪＰ，Ａ) 特公 昭63−18419（ＪＰ，Ｂ２) ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tadahiro Goda 1-2-1, Wadazakicho, Hyogo-ku, Kobe-shi, Hyogo Pref. Mitsubishi Electric Corporation Control Company (72) Inventor Toshiharu Narita Hyogo-ku, Kobe-shi, Hyogo 1-1-2 Tazakicho Mitsubishi Electric Corporation Control Plant (72) Kunio Matsuzawa 1-10-7 Marunouchi, Kofu City, Yamanashi Prefecture Tokyo Electric Power Company Yamanashi Branch (72) Inventor Toshio Kasahara Tochigi 1-1-11 Baba-dori, Utsunomiya City, Tokyo Electric Power Company Tochigi Branch (56) References JP-A-64-1430 (JP, A) JP-A-55-147923 (JP, A) JP-A-63-11025 ( JP, A) JP-B 63-18419 (JP, B2)
Claims (1)
数偏差を検出し、その周波数偏差が負荷脱落に起因して
発生した周波数上昇現象により、予め定めた設定時間継
続して周波数偏差の設定基準値より大きいとき、動作信
号を出力する周波数偏差検出リレーと、上記電力系統の
電圧及び電流に基づいて該電力系統の有効電力を演算し
て一定時間分記憶し、その記憶値と現在値とから上記負
荷脱落前後の有効電力偏差を求め、この有効電力偏差が
上記周波数偏差検出リレーの設定時間より長く設定され
た時間継続して有効電力偏差の設定基準値より大きいと
き、動作信号を出力する電力偏差検出リレーと、この電
力偏差検出リレー及び上記周波数偏差検出リレーの少な
くとも一方からの動作信号を出力するOR回路とを備え、
このOR回路からの動作信号によって所定の発電機を上記
電力系統から解列するようにしたことを特徴とする電源
制限用保護継電器。A frequency deviation of a power system to which a plurality of generators are connected is detected, and the frequency deviation is caused by a frequency rise phenomenon caused by a load drop, and the frequency deviation is continuously determined for a predetermined set time. When the value is larger than the set reference value, the frequency deviation detection relay that outputs an operation signal, and the active power of the power system based on the voltage and current of the power system are calculated and stored for a fixed time, and the stored value and the current value are stored. From this, the active power deviation before and after the load drop is calculated, and when this active power deviation is longer than the set time of the frequency deviation detection relay and is continuously larger than the set reference value of the active power deviation, an operation signal is output. A power deviation detection relay, and an OR circuit that outputs an operation signal from at least one of the power deviation detection relay and the frequency deviation detection relay,
A protection relay for limiting power supply, wherein a predetermined generator is disconnected from the power system by an operation signal from the OR circuit.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP1024631A JP2728486B2 (en) | 1989-02-02 | 1989-02-02 | Power limiting protection relay |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP1024631A JP2728486B2 (en) | 1989-02-02 | 1989-02-02 | Power limiting protection relay |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH02206332A JPH02206332A (en) | 1990-08-16 |
| JP2728486B2 true JP2728486B2 (en) | 1998-03-18 |
Family
ID=12143483
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP1024631A Expired - Fee Related JP2728486B2 (en) | 1989-02-02 | 1989-02-02 | Power limiting protection relay |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2728486B2 (en) |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS55147923A (en) * | 1979-05-07 | 1980-11-18 | Tokyo Shibaura Electric Co | Method of analyzing defective machine of generating facility |
| JP2653428B2 (en) * | 1986-06-30 | 1997-09-17 | 東京電力株式会社 | Power system stabilizer |
| JPS6318419A (en) * | 1986-07-10 | 1988-01-26 | Nec Corp | Frequency dividing circuit for microcomputer |
| JPS641430A (en) * | 1987-06-22 | 1989-01-05 | Hitachi Ltd | Inter-system checking device |
-
1989
- 1989-02-02 JP JP1024631A patent/JP2728486B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH02206332A (en) | 1990-08-16 |
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