-Yes, the transformer draw current when secondary open. Because, the secondary of the
transformer is open, the primary draws only no-load current, which will have some copper loss.
Therefore, power is no longer transferred from primary to secondary in this approximation, and
negligible current goes through the secondary windings.Some current will flow through the primary as
well as secondary to magnetise the core to maintain the internet relaship between primary &secondary
winding as the winding consist of small resistance it is neglected practically hence the current will at at
no load also which is small in magnitude compared to the full load current.Thta is why we says that
transformer draws current when secondary is open.
Current transformers produce a ratio of primary current in the secondary. If the secondary of a CT is open circuited, and primary current is flowing, the CT will try to push that same ratio of current through the secondary open circuit. This causes secondary voltage to climb until it the secondary open circuit flashes over. This can often damage the CT.
In general there is no reason why it should not be, though there may be special situations. Perhaps there is confusion with CURRENT transformers which must not be left open circuit because of the high voltages which they will produce. it may trip the CB. although there is no faults but a high current called Inrush current is flow when the the power transfomer energized while its secondry circuit is open
I am assuming the question is about the power / distribution transformer and not the current transformer. The primary current is a function of load connected on secondary. With the open secondary, there is no load, no current, it is open circuit. Hence no primary current. However there is always some small amount of no load current in the primary winding.
Current transformers (CTs) -together with voltage (or potential) transformers- are 'instrument transformers'. CTs are used to enable large currents flowing in high-voltage systems to be measured, while electrically-isolating the ammeter (termed a 'burden') from the h.v. system. They are also used to monitor h.v. currents for high-voltage protection systems. Before disconnecting its burden, the secondary of a CT must be short-circuited, and remain short-circuited until after the burden has been replaced. This is because a dangerously-high voltage will appear across the open terminals of any energised CT.
With the secondary not supplying any load, there is no secondary current and the primary current will be a low-value magnetising current. So, the copper losses, (I2R) will be insignificant.
Current transformers produce a ratio of primary current in the secondary. If the secondary of a CT is open circuited, and primary current is flowing, the CT will try to push that same ratio of current through the secondary open circuit. This causes secondary voltage to climb until it the secondary open circuit flashes over. This can often damage the CT.
A: If the transformer is connected to a power input of course it will draw current. The primary is a long wire it has own resistance wrap around an iron core. Of course there will be primary current whether there is a load on the secondary or not.
A current transformer's secondary must never be open-circuited. If the instrument fed by a CT needs to be removed, then the secondary terminals must be short-circuited first. This is because a large, and potentially-dangerous, secondary voltage will appear across an open-circuited CT. Normally, a set of links is provided at those terminals for this purpose.
In general there is no reason why it should not be, though there may be special situations. Perhaps there is confusion with CURRENT transformers which must not be left open circuit because of the high voltages which they will produce. it may trip the CB. although there is no faults but a high current called Inrush current is flow when the the power transfomer energized while its secondry circuit is open
A secondary current of 0 would suggest to me that the secondary circuit is open. A normally operating circuit with zero current flow would be very unusual. No load in secondary circuit. No secondary current can also be attributed to the primary power source open or an open primary winding.
I am assuming the question is about the power / distribution transformer and not the current transformer. The primary current is a function of load connected on secondary. With the open secondary, there is no load, no current, it is open circuit. Hence no primary current. However there is always some small amount of no load current in the primary winding.
Current transformers (CTs) -together with voltage (or potential) transformers- are 'instrument transformers'. CTs are used to enable large currents flowing in high-voltage systems to be measured, while electrically-isolating the ammeter (termed a 'burden') from the h.v. system. They are also used to monitor h.v. currents for high-voltage protection systems. Before disconnecting its burden, the secondary of a CT must be short-circuited, and remain short-circuited until after the burden has been replaced. This is because a dangerously-high voltage will appear across the open terminals of any energised CT.
Current transformers should be shorted off load to prevent the voltage induced in the secondary winding from reaching high levels that could lead to insulation breakdown. When left open circuit, the induced voltage could damage the transformer or the connected equipment. Shorting the secondary winding ensures a low impedance path for the induced voltage to circulate and dissipate harmlessly.
Unless a burden (i.e. meters, relays, etc.) is connected to the CT, current transformers should always be shorted across the secondary terminals. The reason is very high voltages will be induced at the terminals. Think of the CT as a transformer, with a 1 turn primary and many turns on the secondary. When current is flowing through the primary, the resulting voltage induced in the secondary can be quite high, on the order of kilovolts. When a CT fails under open circuit conditions, the cause of failure is insulation breakdown, either at the shorting terminal strip, or at the feedthrough (in the case of oil filled apparatus), because the distances between terminals are not sufficient for the voltages present.
You never ever ever ever under any condition open the secondary when primary current is flowing.
A current transformer will always attempt to push a ratio of the primary current through the secondary. So if there is primary current flowing, and you open circuit the secondary, the CT will attempt to build up voltage to the point where the correct amount of secondary current can flow through the open circuit (meaning you will get an arc). If it succeeds, you'll have a bright light, and some melted copper, and a very startled person who was unfortunate enough to open circuit the CT. This high voltage can also damage or ruin the CT.
When the secondary of a transformer is opened, there is no longer any load on the transformer. There will be some current flowing in the primary winding, which is needed to induce the voltage in the secondary. This primary current is referred to as the "no load" current, and is indicative of the core losses in the transformer.