UBZ-301 Universal Protection Unit and Other Electromotor Protection Devices in the Market: Comparative Analysis
The majority of electromotor protection devices in the market (so called current protection) are practically equal in their functional capabilities which seem to be very primitive ones as compared with functional capabilities of an UBZ-301 Unit by NOVATEK-ELECTRO company production.
UBZ-301 Universal Electromotor Protection Units are conceptually new reasonably-priced protection devices for 3-phase AC motors. This is the first time when a protection unit is able to perform full and effective multi-fault motor protection. The UBZ-301 Unit provides protection from all faults in the mains, motor performance-induced faults and internal fault conditions of motor. Application of modern microprocessor-based technology allows to use the wanted operation logic that no protection devices of domestic and foreign production can provide.
The UBZ-301 conceptual distinction from analogous devices by other producers is as follows:
1. Mains voltage fault protection is available. The unit provides phase loss, phase “coincidence”, incorrect phase sequence, phase/line voltage imbalance, unallowable voltage jumps & drops monitoring. This monitoring is generally missing in the units presented in the market. In some of the most expensive foreign units (that cost more than 500 Euro) the mains supply presence and mains voltage presence on all three phases is checked at best before the motor start. In most cases to learn about voltage of poor quality is possible only indirectly, after a current load has been thrown on. The UBZ-301 unit provides voltage measurement not only before the motor start (the load will not throw on at poor voltage) but also after power has been on. Simultaneous independent phase current & mains voltage monitoring allows to detect a type of occurring fault and to provide a different decision-making logic for each fault type. For instance, mains voltage faults can permit the motor restart but internal fault conditions of the motor can forbid the restart.
2. Nominal and operating current setting. For the correct unit operation it’s fundamentally significant to specify a nominal current value of the motor as accurate as possible. The correct specification of the parameter guarantees an effective and reliable decision-making for overloads of different kind and other current faults. This is exactly the stumbling block for all units of domestic production. In some of the domestic units the nominal current is set very roughly, in other units the nominal current setting is impossible at all, in some units it’s possible to set not the nominal current but the maximum operate current. Actually this is overload protection, or the maximum current protection with a time delay: if the current is less than the maximum one but higher than the nominal one the motor goes in overload conditions although the protection will not detect this. For example, a number of domestic protection devices require a nominal load on the motor shift before the start. But producers of these units don’t inform consumers how to do that basically. At the same time according to independent studies the long-term electromotor operation with the load that exceeds the nominal load by 5% in ten times reduces the motor winding life. Thus, when the accurate nominal current setting in the unit is not available the protection provided by the unit happens to be a very coarse one and functionally the unit doesn’t differ from an ordinary thermal relay which is much cheaper. The UBZ-301 allows to set a nominal current with a high degree of accuracy before a load is thrown-on. Nominal current setting is to be performed correcting for load connections (Wye/Delta), ‘cause currents are measured by toroidal current transducers which are put on the load power leads. When the load connection is Wye, the currents correspond to the load phase currents. When load connection is Delta, the load phase currents are 1.73 times less than the currents that flow through power leads.
3. The UBZ-301 Unit operates on RMS current and RMS voltage. No existing protection device provides this possibility. Why is it so significant to make a decision on RMS values, especially RMS phase/line currents? Because current curves, particularly at starts, are not very similar to sine curves. If one makes decision not on RMS values but on some averaged signals, or, what even worse, on peak values as it happens in many other devices, the protection devices either will be tripping falsely or fail to protect effectively the load.
4. Heat overload protection. Application of microprocessor technique enables to use sophisticated mathematical signal processing. In particular, continuous monitoring of RMS current allows to solve the motor heat balance equation. It means that the UBZ-301 analyzes an overload on the base of the previous motor operation data. Thus a previously loaded motor after overload will be stopped quicker than a previously cold one. Other units operate at best on some averaged current-time characteristic curves ignoring previously accumulated motor heat. This approach is especially required not only when load on the motor shaft is changing and overloads are periodically occurring but also when frequent starts take place. In this case the motor can suffer heat overloads even having been in overload area for a short time and periodically returning to the nominal load. Au contraire, the UBZ-301 allows to limit a number of starts per unit time by suitable selection of different Ton values, heat hysteresis considered, because in the intermittent cycle the unit stores heat quantity released at the start of the motor. This is very important because a motor whose load on the shaft is less than the nominal load can overheat through frequent starts. The motor is protected from the heat overload. After the load has been de-energized owing to the heat overload it will automatically be energized again according to heat hysteresis if time delay Ton=0, i. e. the motor must cool down 30% of the stored up heat; according time delay Ton if Ton>0. Heat balance equation is solved continuously in the process of the motor operation and during the motor stops.
5. Balanced/unbalanced phase/line current overload protection is performed on the base of sophisticated decision-making logic. The unit isolates electrical equipment from the running system and/or disables its start when mechanical overloads (symmetrical phase/line current overload) occur, when phase/line current asymmetrical overloads induced by faults inside motor occur; when phase current asymmetry without overload occurs that is induced by insulation fault inside motor and/or power cable.
6. The minimum operating or starting current protection is performed when motor load is lost («dry stroke» for pumps).
7. The UBZ-301 unit is a microprocessor-based digital device with a high degree of reliability and accuracy. Most other units in the market are analogous ones and depend on ambient conditions chiefly on ambient temperature.
8. One of the most significant features of the UBZ-301 for
consumers is its price. All the foreign motor current protection
devices in the market have the start price from 290 Euro. Wholesale
(trade) price for UBZ-301 is less than 100 US$. Actually consumers get
a few products for this price: a voltage relay, a phase monitoring relay,
an isolation monitoring relay, a current monitoring relay, a current
leakage protection device, an overload/underload protection device,
an automatic reset unit with time delays, and so forth.