Barrage type tidal power plants can provide flexibility to the electricity grid thanks to the ability of hydraulic machines to be operated both as pumps and turbines. The added value of a fast switching tidal power plant is investigated within the project “Playing with Current(s)” (PwC), executed by universities, national knowledge institutes, utility companies and turbine manufacturers in The Netherlands. Necessary condition for grid-stabilisation is that a power plant can come online, from zero to full power within a very short timespan. As in the Netherlands power dispatching is done every 15 minutes, within the PwC project the maximum spin-up time is set ambitiously at 10 seconds. This paper covers the investigations of the transient behaviour of a tidal pumpturbine during start-up. As preliminary tests have shown that the full-load, passive ramping-up time of the tidal power plant is in the range of 20-30 seconds, two “kickstart” procedures have been proposed and investigated. During kickstart, the turbine is first operated as a pump to accelerate the water mass inside the duct to the desired full-load speed, and then switched from pump to turbine operation. Results are compared with the analytical solution of a simplified flow differential equation and with tests done with the Tidal Turbine Test Setup at HZ University of Applied Sciences. Results show that a kickstart with a frequency controller may reduce the ramping-up time to less than 10 seconds, which is sufficiently fast to operate the tidal power plant as a grid stabilisation facility.